In late 1984, Morris first appeared in the WWF as a wrestling fan known as "Big Jim" who routinely sat in the front row of live events and who eventually decided to try his hand at wrestling himself. After appearing as a guest on Piper's Pit, Rowdy Roddy Piper offered his services to train him, though he eventually chose to be "trained"' by WWF Heavyweight Champion Hulk Hogan instead of the heel Piper. A series of vignettes were aired on WWF's TV programming in the early weeks of 1985, showing Hogan training Jim and providing him with his first set of wrestling boots. This introduced the character of Hillbilly Jim; a simple-minded, shaggy-bearded Appalachian hillbilly clad in bib overalls, and hailing from Mud Lick, Kentucky. Hillbilly Jim appeared in a few tag team matches with friend Hulk Hogan and had his first high-profile singles match at The War to Settle the Score event on February 18, 1985, in which he defeated Rene Goulet. However, Morris was sidelined by an injury a few days later. At a show in San Diego, he appeared in Hogan's corner in a match between Hogan and Brutus Beefcake. While chasing Beefcake's manager Johnny V around ringside, Morris slipped on a wet spot and injured his knee. To help fill in the six months during his recovery, similarly dressed "family" members Uncle Elmer, Cousin Luke, and Cousin Junior were introduced for Morris to accompany to ringside as a manager.[1]

When his in-ring career resumed, Morris often either tag teamed with his family, or fellow big man André the Giant. He was traditionally matched up against the WWF's monster heels of the era, such as Big John Studd and King Kong Bundy. He also had a short feud with Mr. Fuji and wrestled him in a series of tuxedo matches in late 1986. Hillbilly Jim was generally kept as a "fun" character, rarely getting involved in any serious storylines. His theme music was a folksy barn dance tune called "Don't Go Messin' With a Country Boy", which Morris danced along to with his partners, the ring announcer and/or children from the crowd while the audience clapped along. His first WrestleMania appearance was at Wrestlemania 2 as part of the open invitational battle royal. His next Wrestlemania appearance was a novelty match in WrestleMania III involving King Kong Bundy and midget wrestlers.[3] At Survivor Series '88, Jim teamed with his old mentor Hulk Hogan along with Randy Savage, Hercules and Koko B. Ware to defeat the team of Big Boss Man, Akeem, Ted DiBiase, King Haku and The Red Rooster. Though Jim was eliminated by Akeem, Hogan and Savage would go on to survive and win the match.

Hillbilly Jim also worked as a fill-in for wrestlers who did not appear or who had left the company. John Studd had departed the WWF while in the midst of a major feud with Andre the Giant and Jim was called upon to fill Studd's role. On June 10, 1989, at the Nassau Coliseum Jim scored a huge upset over Andre the Giant defeating him by disqualification. Hillbilly Jim continued to appear regularly in WWF matches until the summer of 1990, getting wins over Haku, Boris Zhukov, Brooklyn Brawler, "Dangerous" Danny Davis, "Iron" Mike Sharpe, and "Playboy" Buddy Rose. His last high-profile match with the WWF was during the April 28, 1990 (taped April 23, 1990) edition of Saturday Night's Main Event XXVI, in which he lost to Earthquake in a squash match that lasted just under 2 minutes. His final match was on August 31, 1990, with a win against Black Bart in Cedar Rapids, IA.[4] In 1992, Hillbilly Jim returned to the WWF as one of the final hosts of WWF Prime Time Wrestling alongside Vince McMahon, Jim Duggan, Bobby Heenan, Mr. Perfect, Sgt. Slaughter and many more until the final episode of Prime Time Wrestling in January 1993.