Morales made his first appearance for the World Wide Wrestling Federation, now known as WWE, on November 21, 1970, by teaming with Chief Jay Strongbow in a draw against The Mongols, Newton Tattrie and Josip Peruzovic, as part of a one-night appearance. Now a full-time member of the WWWF roster, he joined Gorilla Monsoon the following month, scoring a win in a three-fall rematch. In his singles debut, Morales defeated Joe Turco. This was followed by wins over The Black Demon, "The Wolfman" Willie Farkas and Bulldog Brower during the following month. On January 7, 1971, Morales won the vacant WWWF United States Championship by defeating Blassie in a tournament final. A team-up with Gorilla Monsoon also took place in two draws involving The Mongols. On February 8, 1971, Morales defeated Ivan Koloff to win the WWWF World Heavyweight Championship only a month after winning his first individual title within the promotion. The move also vacated the United States Championship. This ignited a series of wins over the likes of Jack Evans and his previous opponents The Black Demon and Bulldog Brower. Subsequently, a series of victories in tag team matches involving Blackjack Mulligan evolved into a feud of single encounters, in which Morales won half a dozen events, before scoring two more team victories along Moonson. Meanwhile, The Wolfman and Bulldog Brower became recurrent enhancement talents during this run. Morales also scored wins over the likes of Beautiful Bobby and Tarzan Tyler, who eventually teamed up with Luke Graham, which turned into a double feud against both. Tyler, The Black Demon, Graham and The Beautiful Bobby were the opponents faced by him during a winning streak that extended throughout the summer. Different tag teams along Monsoon, Jay Strongbow and Manuel Soto experienced similar success. During August 1971, Morales scored several victories over Graham and Tyler, also besting them as a tag team and in a 3-on-3 match that included Lou Albano. However, in his final contest of the month he suffered a loss to Stan Stasiak. In September, Tyler and Graham brought in Jimmy Valiant as a teammate, which led to a series of matches including a win over him in a steel cage. On October 25, 1971, Morales defeated Stasiak in a Texas Death Match. The following month brought wins over Tyler and Valiant, but also included an encounter where he bested Freddie Blassie and a continuation of the feud against Stasiak during the second half. During this timeframe, Rivera joined Morales in the WWWF, becoming part of his usual partners along Monsoon and Strongbow. He closed 1971 by defeating Blassie in a “Roman Gladiator” match, Ray Stevens, Stan Stasiak twice and The Rugged Russians along Rivera
First contender Blassie and Stasiak remained Morales' main rivals in the first two months of 1972, against whom he scored several draws and some wins. Graham, Valiant and Toru Tanaka served as enhancement talents. On February 18, 1972, Morales and Rivera defeated The Rugged Russians, continuing this parallel rivalry. March featured several different matchups, in which he emerged victorious against "Baron" Mikel Scicluna, Smasher Sloan and Rugged Russian #2, while consistently teaming with Rivera against Curtis Iaukea & Scicluna, both of whom he defeated individually throughout April. The following month feuds that ended in Morales earning several victories over Pampero Firpo, Tanaka, Iaukea and Albano. After disposing of Valiant, Graham, Scicluna and Graham again, the feud against Albano continued with wins in regular and steel cage matches. During June 1972, Morales also bested other notable opponents, including Nikita Mulkovitch, Blue Demon and Ernie Ladd. To continue this run, he defeated George Steele in New York. Following wins three wins over Tanaka and more against Firpo, Morales teamed with Sammartino on July 18, 1972, to face the former and Mr. Fuji. The match featured the two most popular wrestlers of the era, but finished in a no contest with both of the involved in a confrontation after Mr. Fuji threw salt in both of their faces, ensuing a fight. A rematch took place, this time in a team with Monsoon, but finished in a draw. Morales defeated both Tanaka and Mr. Fuji by countout and won the following two tag team matches. This was followed by a series involving Steele, Fuji, Ernie Ladd, Chuck O'Connor and "The Spoiler" Don Jardine, none of whom were able to gain an upper hand against him. On September 30, 1972, Morales faced Bruno Sammartino in the first-ever match featuring two fan favorite, technical wrestlers. The crowd favored him, despite Sammartino's large fan base in the city of New York. After 75 minutes of wrestling featuring several near-falls, the contest ended in a draw, when the city's curfew entered in effect. Subsequently, both performers embraced, signifying the end of their rivalry and the reformation of the tag team. However, the lack of a resolution was not well received, the fans were noticeably angry, and some jumped into the dugouts to shake their fists at the wrestlers. The main event of the 1972 Showdown at Shea later became known as "The Match of the Century" and is still regarded as one of the best events in the history of professional wrestling. After scoring a win over The Spoiler, Morales joined Sammartino in a rematch against Tanaka and Mr. Fuji, this time emerging victorious in a three-fall contest.
This was followed with a rematch, this time teaming with André the Giant. The Spoiler remained Morales most common adversary during the following months, which resulted in wins over him and his partner, Buddy Wolfe. Other wrestlers to fail their attempts were Ernie Ladd, The Sheik and Ray Stevens. To close the year, Morales defeated Tanaka individually and in tag team action, before going on to defeat Wolfe on several occasions. On December 2, 1972, he rejoined Rivera in a win. During the first months of 1973, Morales bested Mr. Fuji, Buddy Wolfe and Lonnie Mayne, as well as Hans Schmidt, Lonnie Mayne and Curtis Iaukea. He also teamed along Moonson, Bobo Brazil and Strongbow. A feud with Mayne went on to include a steel cage match. A series against Freddie Blassie concluded with three singles wins for Morales, also including a tag team contest. Throughout April and May, he successfully faced a number of recycled adversaries, including Mayne, Wolfe and Tanaka, along wins over new ones such as Don Leo Jonathan and Mike McCord. Morales also defeated Blassie twice, including a steel cage match. Throughout the summer, he performed mostly as a singles wrestler, gathering wins over Toru Tanaka, Paul Jones, Lonnie Mayne, Jonathan, McCord and George Steele facing them repeatedly in cyclical fashion. This trend was broken with the arrival of August, when Morales bested other figures including Blackjack Lanza and Stan Stasiak. During the month of September 1973, he was placed over Ib Solvang Hansen, McCord, Steele and Fuji. Morales went on to win a series against Lanza and a Texas Death Match involving Stasiak, before having Fuji serve as enhancement talent for the following weeks. He followed this by entering a feud with Stasiak which featured mixed results, but concluded with him dropping the WWWF World Heavyweight Championship on December 1, 1973. Morales' title run lasted 1,027 days, remaining to this date the longest reign by any Latino and the fifth longest overall. Following this, he returned in two tag team matches, before defeating Stasiak twice in three rematches. Morales remained successful as a singles wrestler, gathering wins over Fuji, Eddie Sullivan, Otto Von Heller, Johnny Rodz and Black Gordman during the first half of 1974. During the second half of the year, he bested Nikolai Volkoff and Strong Kobayashi, before exchanging results in a long-running feud against Killer Kowalski. In his final phase of this run for the promotion, Morales was victorious over Butcher Vachon, wrestling his final match on March 1, 1975.
On May 6, 1980, Morales returned to the renamed World Wrestling Federation, defeating Moose Monroe, Frank Savage, Mark Pole, Brute Bernard and Ben Alexander during the course of the following weeks. He formed a tag team with Bob Backlund, which won its first two contests. Meanwhile, Morales continued on his successful run with victories over Ron Shaw, Mikel Scicluna, Tor Kamata, Afa, B.B. Coleman, Johnny Rodz and The Hangman. On August 9, 1980, he won the WWF World tag Team Championship along Backlund by besting Afa and Sika, the Wild Samoans, at the Showdown at Shea 1980. However, they had to forfeit the belts the same night, due to a rule stating that no heavyweight champion could hold a second title at the same time. During the following month, Afa and Kamata served as enhancement talent, while Morales also participated in a battle royale. Afterwards, he went on to defeat several adversaries, including Larry Zbyszko, Scicluna, Afa, Rodz and The Hangman. A series with Patera intensified after a loss, with Morales recovering to defeat him to win the WWF Intercontinental Championship on December 8, 1980. With this win, he became the first man in history to win the Triple Crown Championship, which along his United States Championship reign also meant holding all of the promotion’s titles during his era, a recognition that only he held for almost two decades. Morales also feuded with Sgt. Slaughter, defeating him by disqualification. During the early months of 1981, he continued defeating the likes of The Hangman, Ron Shaw, Jose Estrada and Zbyszko, but tied in contests against St. Slaughter and Stan Hansen. After defeating and drawing with St. Slaughter in another series, Killer Khan became Morales' most recurrent adversary, experiencing more success, while other names such as Greg Valentine and Hansen challenged him occasionally. This was followed by a short feud against The Moondogs, which ended with singles wins over both members of the team. On March 26, 1981, Morales faced Hulk Hogan, dominating throughout the match and winning by count out. The feud with The Moondogs resumed afterwards, with mixed results in tag team competition but another win over Moondog Rex. Another figure that became a mainstay was St. Slaughter, whom he often defeated by disqualification.
Jerry Johnson and Johnny Rodz served as jobbers during this run. After participating in a battle royale won by Angelo Mosca, the two entered a feud, from which Morales emerged victorious. During the month of June, he also scored consecutive wins over his former rivals Killer Khan and Sgt. Slaughter, ending their respective storylines. This led to a feud against Don Muraco, to whom Morales dropped the Intercontinental Championship on June 20, 1981. Two subsequent rematches ended in one win, three losses and a draw. Morales began wrestling and defeating other adversaries, including George Steele, The Executioner and Larry Sharpe, besides the usual low card talents that he had consistently bested previously. However, the feud with Muraco was reignited and he earned two wins and a draw, leading to a titular rematch between them. Morales entered the contest with wins over The Executioner and Greg Valentine, winning the Intercontinental Championship back on November 23, 1981, in a Texas Death Match. With this win, Morales became the first man to hold the Intercontinental title twice, and he held it for fourteen months, the longest reign up until that point. He was successful in four rematches against Muraco, with Valentine systematically becoming his main adversary. In his first bout of 1982, Morales defeated Valentine by disqualification. He was able to dominate Hans Schroeder, Larry Dee and Killer Khan, but drew in another match against Valentine, who also went on to win their next encounter by disqualification. Their series continued with the equitable results of one win, one loss and a draw. To continue, Morales won two consecutive contests, including a Brass Knuckles Alley Fight, but got disqualified in the third. This was momentarily interrupted with a short program against Mr. Fuji, Mr. Saito and Lou Albano, which also featured wins over Rodz and Adrian Adonis. After being resumed, Morales won two more matches over Valentine, once again being disqualified in the third, before coming back to win in a Texas Death Match. He then entered a winning streak, during which he defeated The Black Demon twice, Jesse Ventura by count out, Adonis thrice, Fuji and Valentine four times, two of these being Brass Knuckles Matches and other a Street Fight. This came to an end when Morales was disqualified against Jimmy Snuka. He wrestled Valentine three more times, winning in a Brass Knuckles Match and by count out.
During the summer of 1982, Morales feuded with Bob Orton, Jr., gaining the upper hand after being disqualified in the open bout. Estrada, Saito and Swede Hanson were also bested during this time. However, this streak was also ended in a count out loss to Snuka. In September, Morales won contests over Rocky Cole and Scicluna, but was counted out against Buddy Rose, which led to a draw in a rematch. He opened the following months with victories in matches featuring Bob Bradley, Tony Russo and Swede Hanson, but was counted out in a challenge by Billy Graham. Morales continued his feud with Buddy Rose, defeating him by disqualification. Two more matches against Graham ended in a draw and a disqualification loss. Afterwards, Morales was involved in a no contest and a double disqualification draw with Rose, going on to close with two consecutive wins. During the month of November, he divided honors with Graham, also scoring victories over Tony Russo and Fuji. On December 28, 1982, Morales wrestled Don Muraco to a double disqualification draw. On his first match of 1983, the result was repeated, this time in a match involving Graham. The following weeks brought wins over Sammy Sanders, Bob Bradley, Fuji and Rose, but also losses to Graham and Muraco, most of which were by count out or disqualification. After besting Graham in another bout, Morales dropped the Intercontinental Championship to Muraco on January 22, 1983. However, he countered by winning a rematch, also defeating Graham before losing a second rubber match. Afterwards, Morales gained wins over Swede Hanson, Bob Bradley, Victor Rivera, Buddy Rose, Huertas Gonzalez and Fuji. He also emerged victorious from a feud with Graham, winning the mayority of their encounters. Morales and Muraco went on to exchange results, but neither one was able to dominate cleanly, with most wins being consequence of count outs and disqualifications. Meanwhile, he bested Eddie Carson and participated in occasional multi-wrestler team matches.
Morales entered the 1985 King of the Ring tournament, besting Johnny V in the opening contest before receiving a bye during the quarterfinals. However, he was eliminated by Muraco in the semifinals. During this timeframe, Tito Santana became his occasional tag team partner. Individually, Morales went on to defeat M.X several times, Gibbs, Lombardi and Barry O twice, Rene Goulet four times and Tiger Chung Lee. He was also successful in two team matches along Santana. On September 12, 1985, Morales bested Muraco in New Jersey. The following night he claimed a win over Valentine. Morales defeated Gob Orton, Jr., Goulet and Barry O to conclude the month. October began with a winning streak which featured Les Thornton and Matt Borne along enhancement talent, but which was stopped by "The Missing Link".
Morales made his following appearance in a WWF event held in San Juan, Puerto Rico, where he defeated The Spoiler. The second half of the month brought wins in two matches along Santana and singles success over opponents that he had previously wrestled. This pattern continued in November, when Morales and Santana exchanged results against Valentine and Brutus Beefcake. Individually, he gained victories over several familiar performers including Lee, Barry O, Gibbs and The Spoiler, also winning a series against Alexi Smirnoff and losing a single time to Orton. Contests including Moondog Spot, Thorton and Lee ended in the same fashion, with Morales going on to win a rematch over Orton. On December 12, 1985, Goulet scored a rare win over him. In turn, Morales ended the year with wins over Matt Borne, The Spoiler, Smirnoff, Barry O and Mike Sharpe, in the process successfully teaming with Santana. He won his first two contests of 1986 Moondog Spot and Lee, before losing to Terry Funk. This was followed by a series of tag team matches along Santana and Danny Spivey, which ended with a 2-1 balance. After besting two jobbers, Morales teamed with Steve Gatorwolf to defeat Valentine and Beefcake. After four more wins over his regular opponents, he lost to Orton. This pattern was repeated once more, but this time Morales earned a disqualification victory over Orton after winning the first four contests. Concurrently to this series, he was involved in a 3-on-3 match. On February 15, 1986, Morales defeated Bret Hart in Phoenix, Arizona. This was followed with wins over Goulet, Thorthon, Steve Lombardi and a successful feud against Orton. Morales made his only WrestleMania appearance in 1986 when he was a part of a 20-man invitational battle royal at WrestleMania 2. After two tag team victories along Santana, Morales defeated Hercules and Beefcake among others. This was followed by a prolonged series with both members of the Moondogs, from which he emerged victorious. On May 17, 1986, Morales defeated The Iron Sheik in a WWF return to California. His tag team with Santana remained successful, winning their contests throughout the summer. Meanwhile, Morales earned wins over Paul Christy, Roger Kirby, Lee, The Iron Sheik and Hercules, but began to lose more often against opponents such as Jake Roberts, King Kong Bundy and Savage. Like the year before, he entered the King of the Ring tournament, advancing with a win over Rudy Diamond. Morales advanced further by besting Mike Rotundo in the quarterfinals and Nikolai Volkoff in the semifinals, but lost the final to Harley Race. The following months brought mixed results, with wins over Muraco and Jim Neidhart but losses to Hercules and Adrian Adonis.
Morales recovered by defeating Savage three times and Gibbs once, while drawing with Orton before losing a rematch to Race. He entered the Sam Mushnick Memorial Tournament, winning his matchup against Funk in the opening round before being eliminated by Beefcake in the quarterfinals. On September 20, 1986, Morales defeated Jake Roberts. His next two feuds featured him getting disqualified and defeated by Muraco, exchanging results with Hercules and dominating Moondog Rex. However, his next series against Kamala saw him being counted out and pinned. A feud with Orton ended in similar fashion. Morales' team with Santana suffered the same fate, losing twice and participating in a double count out draw. Two rivalries involving Hercules and Steve Lombardi ended with mixed results. Afterwards, Morales won contests over The Red Demon, Lombardi and Sivi Afi, while losing to Muraco and being counted out against Savage. The following month opened with victories over Sika, Muraco and Lombardi, but also included loses to Dino Bravo, Butch Reed, Kamala and Hercules. In December, Morales bested Jimmy Jack Funk, Volkoff, Frenchy Martin and Bravo, but also featured an unsuccessful rivalry with Race. He opened 1987 with a win over Bret Hart, before teaming with Santana twice with mixed results. However, now 44 years old Morales was entering his final year as an active wrestler, now being moved back in the card. He lost a series of matches against Bravo, but bested Muraco before entering a feud with Nick Kiniski that featured several draws before he gained the upper hand in the final bout. Despite this, during this stage of his career Morales was unable to gain wins over the likes of King Kong Bundy and Bravo, unsuccessfully challenging the new Intercontinental Champion, The Honky Tonk Man, on several dates. Some wrestlers that he had bested in the past, such as Butch Reed or Sika were also booked over him, along strong adversaries such as Jake Roberts, Bravo, Oron and Paul Orndorff. His wins over this timeframe were over Moondog Spot, Sika and Jimmy Jack Funk. On March 8, 1987, Morales teamed with Danny Spivey in the quarterfinals of a march for the World Tag Team Championship, but were eliminated by Rick Martel and Tom Zenk. May was marked by several unsuccessful matches that formed part of a rivalry with Ron Bass, but finished with a win over Lombardi. Morales and Santana teamed twice more, but were unable to overtake the team of Haku and Tama, however, he subsequently joined Jim Brunzell, being successful over The Hart Foundation, Hart and Neidhart. During July, he bested Martin twice, also losing to One Man Gang and Orndorff. Morales made a final in-ring appearance by participating in a battle royale held on November 16, 1987.
Following his retirement from the squared circle, Morales became a commentator for WWF's Spanish-language programming. Morales was inducted into the WWF Hall of Fame as part the 1995 class.