John Steele Hill was a Canadian professional wrestler best known under the ring names Guy Mitchell, The Stomper and "Gentleman" Jerry Valiant. During his career, he held the top singles titles in Australia and Vancouver, and competed in WWE where he won the WWE World Tag Team Championship.

Hill became a professional wrestler in 1959 after working out for a year at both Al Spittles's and Jack Wentworth's gyms in Canada. He traveled to the United States in 1960 in the hopes of making more money. At the beginning of his career, Hill wrestled under the ring name Guy Hill. While wrestling for Georgia Championship Wrestling in 1961, however, a news reporter accidentally referred to him as Guy Mitchell, and Hill was forced to take on the new name. Under his new identity, Mitchell held the Georgia version of the NWA Southern Heavyweight Championship for one week. Shortly thereafter, he teamed with Bob Rasmussen to win the Georgia version of the NWA Southern Tag Team Championship.

While wrestling in the Australian World Championship Wrestling, he used the ring name The Destroyer and wrestled under a mask. On September 3, 1966, he defeated Bearcat Wright to win the IWA World Heavyweight Championship. The Destroyer's mask was eventually removed, and he announced to the audience that his name was John Hill. After leaving Australia, he began competing in Toronto, Ontario in 1967 as The Assassin.

After wrestling as a heel for four years in Toronto, The Assassin feuded with The Sheik, losing a death match in July 1971. The Sheik won the match and removed The Assassin's mask, revealing him to be Guy "Stomper" Mitchell. While wrestling as a heel in Toronto, Hill also competed as a babyface in Detroit, Michigan. Because the name Mitchell was already being used by another wrestler, WWA owner Dick the Bruiser gave him the ring name The Stomper. The Stomper teamed with Ben Justice and won the Detroit version of the NWA World Tag Team Championship. The team feuded with The Fabulous Kangaroos (Al Costello and Don Kent), who were managed by George "Crybaby" Cannon. During this feud, The Stomper suffered a kayfabe (storyline) injury when the Kangaroos broke his leg. Because he could not wrestle in Detroit while he was supposedly recovering, Hill wrestled in Japan for several months.

Upon his return to Detroit, The Stomper and Justice continued their feud with the Kangaroos. The teams faced each other in a tournament final for the vacant tag team championship, which the Kangaroos won. The following year, The Stomper and Justice regained the title belts by defeating the Kangaroos. They held the belts for five months, and The Stomper had one last reign as champion when he teamed with Bobo Brazil to win the title for the third time on July 21, 1973. They eventually dropped the belts to Ben Justice and his new partner, Killer Brooks.

In 1979, he was brought into WWE as Jerry Valiant after Jimmy Valiant contracted hepatitis With Johnny Valiant, he held the WWE Tag Team Championship. After Jimmy recovered, the three Valiants worked in six-man tag matches, and sometimes eight-man tag matches with manager Lou Albano. After eight months in WWE, Hill split from the Valiants and left the area. He returned as a solo prelim wrestler and referee in 1984 when the WWE would use his ring at shows in Indiana, Missouri, Michigan and Kansas.