In the early 1960's, Maurice "Mad Dog" Vachon was recruited to the American Wrestling Association. Upon debuting, Vachon immediately established himself among the promotion's top box-office draws as fans despised his vicious, mauling tactics; and he thus made the perfect opponent for the All-American Verne Gagne, as the two rivals soon commenced an ongoing battle that would persist on for nearly 20 years. On May 2, 1964, Vachon stunned audiences when he upset Gagne for the AWA World Heavyweight Title, and although Gagne regained the belt just two weeks later, Mad Dog again recaptured the title when he defeated Gagne on October 20 in Minneapolis. Between 1964–67, Mad Dog Vachon would ultimately hold five reigns as the AWA World Champion while taking on all comers within the promotion's massive territory, including Gagne, Mighty Igor Vodic, as well as the legendary powerhouse duo of Crusher Lisowski and Dick the Bruiser.
Mad Dog Vachon's final AWA title reign came to an end on February 26, 1967, at the hands of his nemesis Verne Gagne. Vachon would soon return to the AWA, where he resumed his fierce battles with The Crusher and Dick the Bruiser, while forming a highly successful and dangerous tandem with his brother Paul "Butcher" Vachon. On August 30, 1969, the Vachons defeated Crusher & Bruiser for the AWA World Tag Team Titles; and the following year, the two battled again in a famous steel cage match at Chicago's Comiskey Park (where the Vachons again emerged victorious).
After two decades as one the wrestling's most evil characters, the fans began to rally behind the "Mad Dog" in the late 1970's when he formed an unexpected and odd friendship with ex-archrival Verne Gagne. The unlikely partners made for an impressive tag team, and on June 6, 1979, they beat Pat Patterson and Ray Stevens to capture the AWA tag titles, which they held for over a year before losing to Jesse Ventura and Adrian Adonis. When the AWA began looking to younger stars like Rick Martel and Curt Hennig, Vachon jumped to the World Wrestling Federation in 1983. While his age and lack of size did not make for a good mix in the emerging "Hulkamania" era, the now-face (fan favorite) Vachon was usually included at WWF house shows in the Midwest and Quebec. He wrestled for the WWF in Canada regularly until 1986, and even contributed to the WWF's French programming by doing a weekly interview segment in French titled Le Brunch a Mad Dog.
In 1985, he appeared as cornerman for AWA World Champion Rick Martel when Martel was challenged by Boris Zhukov in several title bouts in Canada, getting involved in one match on September 19, 1985 in Winnipeg and fighting off Zhukov and his manager, Chris Markoff, after Markoff interfered and helped Zhukov attack Martel, while in a later rematch between Martel and Zhukov held in a steel cage on November 14, 1985 in the same city, Markoff was neutralized by being handcuffed to Vachon.
He appeared at the WWF pay-per-view In Your House 7, that was held in Omaha. He was sitting in the front row near ringside, when his artificial leg was ripped off by Diesel and used as a weapon by Shawn Michaels. In addition, he and longtime rival The Crusher made an appearance at the 1998 Over the Edge pay-per-view, in a segment where the two legends were mocked by Jerry Lawler, including Lawler trying to steal the artificial leg. Crusher and Mad Dog then punched Lawler out of the ring.
On March 27, 2010, he was inducted into the WWE Hall of Fame.
On November 21, 2013, Vachon passed away.