Jim Neidhart, best known over a 24-year pro wrestling carer as "The Anvil" and the father of current WWE superstar Natalya, died Monday. He was 63.

The news was first reported by Neidhart's former in-ring rival B. Brian Blair on Twitter and later confirmed by WWE. No cause of death has been announced at this  time.

Neidhart reached his highest level of success and celebrity as one half the two-time WWF tag team champion Hart Foundation in the late 1980s alongside his real-life brother-in-law Bret Hart.  The 6-foot-2, 280-pound native of Tampa, Florida, married Hart's sister Ellie in 1979. He is survived by their three daughters.

Although Neidhart is not a member of the WWE Hall of Fame and hasn't regularly been featured in storylines or appearances as a WWE legend, he did have a recurring role alongside Natalya in recent years on the E! reality show "Total Divas." 

After the end of his in-ring career, Neidhart battled substance abuse issues, which included arrests and multiple trips to rehab. Former WWE wrestler Chris Nowinski, a Harvard graduate who has become a crusader for concussion research, revealed in a July Instagram post that Neidhart was battling Alzheimer's disease. That post has since been edited.

A former football and track & field star who had a brief stint in the NFL, Neidhart was trained in the infamous Calgary basement (known simply as "The Hart Dungeon") by father-in-law Stu Hart. He went on to play the role of powerhouse with the Hart Foundation, perfectly complementing Bret's in-ring technical prowess with a variety of physical moves including powerslams and spinebusters. 

Neidhart's best skill as a member of the Hart Foundation, however, may have been his ability to play a dastardly heel thanks to his trademark evil laugh and long goatee that he regularly stroked while delivering promos. 

The Hart Foundation made its pay-per-view debut at WrestleMania II in 1986 by being the last two eliminated by Andre the Giant in a 20-man battle royal that featured NFL players. Nine months later, the duo won their first WWF tag team titles by defeating The British Bulldogs on an episode of WWF Superstars thanks to the help of heel referee Danny Davis; the feud continued through WrestleMania III in 1987. 

Neidhart spent most of the 1990s as a singles wrestler, including brief stints with New Japan Pro-Wrestling, WCW and ECW. He returned to WWF in 1994, and after one of many firings by the company shortly after, returned in 1996 as the masked wrestler named Who. Neidhart would revive the Anvil gimmick in 1997, however, and returned to WWF as part of the new Hart Foundation, a stable of Canadian sympathizers who backed Bret in his WWF championship feud against "Stone Cold" Steve Austin. 

The new faction debuted on an April 1997 episode of Raw, as Neidhart joined Brian Pillman, along with his real-life brother-in-laws Bret Hart, Davey Boy Smith and Owen Hart to attack Austin. The feud did big business for WWF at the peak of the "Monday Night Wars" feud against rival WCW, though Neidhart's push came to an end shortly after the "Montreal Screw Job" that November. Bret is the only member of the reformed Hart Foundation still alive.

Although Neidhart would eventually follow Bret to WCW after being released in December 1997, his career as an elite performer ended shortly after. His last in-ring performance for WWE came in 2007 on the 15th anniversary episode of Raw when he competed in a battle royal. Neidhart also wrestled Jay Lethal in a 2009 TNA match after answering his open challenge to wrestling legends.

Neidhart's daughter Natalya, real name Natalie, is a former WWE SmackDown women's champion and WWE Divas champion. She is presently on the Raw roster and featured weekly on television.