In 1982, Vincent J. McMahon sold the World Wide Wrestling Federation to his son, Vince McMahon As McMahon began to expand his newly acquired promotion to the national level, he required his wrestlers to appear exclusively for him. McMahon signed Roussimoff to these terms in 1984, although he still allowed him to work in Japan for New Japan Pro-Wrestling (NJPW).

Roussimoff feuded with Big John Studd over which of the two men was the "true giant" of wrestling. Throughout the early to mid-1980s, Roussimoff and Studd fought all over the world, battling to try to determine who the real giant of wrestling was. In 1984, Studd took the feud to a new level when he and partner Ken Patera knocked out Roussimoff during a televised tag-team match and proceeded to cut off his hair. After gaining revenge on Patera, Roussimoff met Studd in a "body slam challenge" at the first WrestleMania, held 31 March 1985, at Madison Square Garden in New York City. Roussimoff slammed Studd to win the match and collect the $15,000 prize, then proceeded to throw cash to the fans before having the bag taken from him by Studd's manager, Bobby "The Brain" Heenan.

At WrestleMania 2 on 7 April 1986, Roussimoff continued to display his dominance by winning a twenty-man battle royal which featured top National Football League stars and wrestlers. last eliminated Bret Hart to win the contest.

Following a final tour with New Japan Pro-Wrestling in mid-1986, and a win in Austria over CWA World champion Otto Wanz, appearing exclusively with the World Wrestling Federation.

After WrestleMania 2, Roussimoff continued his feud with Studd and King Kong Bundy. Around this time, Roussimoff requested a leave of absence to tend to his health, since the effects from his acromegaly were beginning to take their toll, as well as to tour Japan. He had also been cast in the film The Princess Bride. To explain his absence, a storyline was developed in which Heenan—suggesting that Roussimoff was secretly afraid of Studd and Bundy, whom Heenan bragged were unbeatable—challenged Roussimoff and a partner of his choosing to wrestle Studd and Bundy in a televised tag-team match. When Roussimoff failed to show, WWF president Jack Tunney indefinitely suspended him.[58] Later in the summer of 1986, upon Roussimoff's return to the United States, he began wearing a mask and competing as the "Giant Machine" in a stable known as the Machines.[18] Big Machine and Super Machine were the other members; Hulk Hogan (as "Hulk Machine") and Roddy Piper (as "Piper Machine") were also one-time members. The WWF's television announcers sold the Machines—a gimmick that was copied from the New Japan Pro-Wrestling character "Super Strong Machine", played by Japanese wrestler Junji Hirata,[59] —as "a new tag-team from Japan" and claimed not to know the identities of the wrestlers, even though it was obvious to fans that it was Roussimoff competing as the Giant Machine. Heenan, Studd, and Bundy complained to Tunney, who eventually told Heenan that if it could be proven that Roussimoff and the Giant Machine were the same person, Roussimoff would be fired. Roussimoff thwarted Heenan, Studd, and Bundy at every turn. Then, in late 1986, the Giant Machine "disappeared" and Roussimoff was reinstated. Foreshadowing Roussimoff's heel turn, Heenan expressed his approval of the reinstatement but did not explain why.