Wrestling legend Jim “The Anvil” Neidhart died Monday morning at the age of 63. The news prompted both current and former WWE superstars to take to social media and mourn the death of the wrestler.

Neidhart might be best-known for teaming with brother-in-law Bret Hart as the Hart Foundation in the late 1980s and early 1990s. Bret Hart expressed his sorrow over Neidhart’s death, as did the likes of Ric Flair, The Iron Sheik and other wrestlers that are among the biggest names that have ever competed inside the squared circle.

“Jim Neidhart was a great athlete. He was the power & strength of The Hart Foundation. I loved their finishing maneuver. Celebrate his life. Watch his matches today. My heart hurts for his daughters, wife & @TJWilson. There is only one #Anvil,” tweeted former WWE and ECW wrestler Tommy Dreamer.

“Sad to hear about the passing of Jim Neidhart,” tweeted former WCW president Eric Bischoff. “Condolences to his family, friends and fans. Jim was an important part of the landscape during one of the most important periods in the industry. RIP Jim.”

Neidhart is the father of current WWE superstar Natalya and the father-in-law of former WWE wrestler Tyson Kidd. He married the daughter of WWE Hall of Famer Stu Hart, by whom he was trained in the infamous Hart Dungeon.

Years after tagging with Bret Hart, the two wrestlers joined forces with Owen Hart, Davey Boy Smith and Brian Pillman to form the new Hart Foundation. Bret Hart is now the only member of the stable that is still alive.

Neidhart left WWE in 1997, though his wrestling career didn’t end there. He headed to WCW, along with Bret, where he performed for just a few months.

Neidhart wrestled with WWE for the last time in 2007. He made appearances in recent years on “Total Divas,” of which Natalya is a cast member.