At Newport Harbor High School, Neidhart first gained athletic acclaim for his success in strength-oriented track and field events.

After graduating from high school,[7] Neidhart pursued a career in the National Football League (NFL), where he played for the Oakland Raiders and Dallas Cowboys in practices and preseason games.

[8] Following his release from the Dallas Cowboys, Neidhart traveled to Calgary to train with Stu Hart and pursue a career in professional wrestling.

Stu Hart, seeking publicity for Neidhart, promised him $500 to enter and win an anvil toss at the Calgary Stampede.

Initially a singles wrestler, managed by Mr. Fuji, Neidhart debuted on January 21, 1985, in Madison Square Garden, defeating Tony Garea.

[1] The Hart Foundation won their first WWF World Tag Team Championship on the February 7, 1987, episode of WWF Superstars (taped January 26) from The British Bulldogs (Davey Boy Smith and The Dynamite Kid), with the help of referee Danny Davis, who was continually "distracted" by checking on Dynamite (laid out of the match early by a megaphone shot from Jimmy), allowing the challengers to double-team Smith.

They lost the titles on the November 7 episode of Prime Time Wrestling (taped October 27), to Strike Force (Rick Martel and Tito Santana).

Neidhart eventually joined Bret's side in the feud with Brown causing a rift between the team and manager Jimmy Hart.

[1] On October 30, 1990, The Rockers (Shawn Michaels and Marty Jannetty) defeated The Hart Foundation in a two out of three falls match in Fort Wayne, Indiana, to seemingly win the title.

[16] The Rockers defended the WWF Tag Team title against Power and Glory (Paul Roma and Hercules) on November 3, 1990.

Neidhart returned to WWF television on the November 9, 1991 episode of Superstars of Wrestling, donning new parachute pants with checkerboard designs.

The New Foundation wrestled their final match on February 15, 1992; Neidhart was fired the next day after refusing to take a drug test and throwing a television monitor backstage.

After defeating Mustapha Saed on the next episode, Neidhart teamed with Junkyard Dog for the next, again beating Chick Donovan and Rip Rogers.

Neidhart and The Junkyard Dog beat Paul Orndorff and Dick Slater by disqualification on the June 5 WCW Saturday Night.

Later that night, Neidhart reappeared at ringside again during Owen Hart's King of the Ring tournament final against Razor Ramon.

Neidhart claimed he'd only helped Bret keep the WWF World Heavyweight Championship at King of the Ring so Owen could take it from him.

After Bret won the match, Neidhart entered the cage, locked it and helped Owen beat him down, while the Hart family members tried to climb over it and save him.

Neidhart joined Owen on Shawn Michaels' team, The Teamsters, to face Razor Ramon and The Bad Guys in an elimination match at Survivor Series.

[30] On the July 6, 1996, episode of Superstars, Neidhart returned to the WWF as the masked heel "Who", a gimmick designed for commentators Vince McMahon and Jerry Lawler to make "Who's on First?

On July 6 at In Your House 16: Canadian Stampede in Bret's hometown Calgary, The Hart Foundation defeated the American team of Stone Cold Steve Austin, Ken Shamrock, Goldust and The Legion of Doom.

[1] After Bret and Davey Boy Smith left the WWF on bad terms because of the Montreal Screwjob at Survivor Series.

D-Generation X (DX) leader and WWF Champion Shawn Michaels offered Neidhart a spot in the group on the November 24 episode of Raw Is War.

After the match, DX attacked Neidhart once again and spray-painted "WCW" on his back and signifying him following Bret Hart to World Championship Wrestling.

In September 1998 at Fall Brawl '98: War Games, Neidhart and the British Bulldog defeated The Dancing Fools in a tag team match.

[34] Following his departure from WCW, Neidhart largely retired from the ring, but continued to make sporadic appearances in independent shows.

On January 17, 2003, he lost to Jim Duggan at Border City's main event at Algonquin College in Ottawa, Canada.

[36] Neidhart's last known match was on March 5, 2016, when he teamed with Koko B. Ware and Frankie the Pizza Guy as they defeated Nikolai Volkoff, Clay Dasher and Shawn Andrews at a BCW event in Williamsport, Pennsylvania.

[40] Neidhart and wife, Ellie Hart had three daughters; one, Natalie Neidhart-Wilson, is a professional wrestler under the ring name "Natalya", currently signed to WWE.

[41] According to TMZ, Neidhart's wife Elizabeth told investigators that on August 13, 2018, he was having problems sleeping and got out of bed to adjust the thermostat.

[43] He died at the scene at age 63, with the Pasco County Sheriff's Office stating to TMZ that their preliminary investigation believed he hit his head and succumbed due to his injuries, with foul play not being suspected.