Legendary Chicago Bears running back Gale Sayers has died at 77 years old.

The cause of Sayers’ death was complications of dementia and Alzheimer’s disease, according to his son Guy Bullard, The New York Times reports. Sayers died at his home in Indiana.

One of the greatest players in NFL history, Sayers had a brief but spectacular career. Sayers led the league in rushing twice during a career that lasted from 1965 to 1971. He set a record as a rookie that still stands today with six touchdowns in one game.

Sayers was forced to retire early because of knee injuries. He was inducted into the Pro Football Hall of Fame at 34 years old, becoming the youngest player to receive the honor.

“All those who love the game of football mourn the loss of one of the greatest to ever play this game with the passing of Chicago Bears legend Gale Sayers,” Hall of Fame president and CEO David Baker said in a statement. “He was the very essence of a team player – quiet, unassuming, and always ready to compliment a teammate for a key block. Gale was an extraordinary man who overcame a great deal of adversity during his NFL career and life.”

Sayers is best known by many for his relationship with Brian Piccolo, a Bears’ running back who died from cancer at 26 years old. Their friendship was detailed in the 1971 TV movie “Brian’s Song.”

Gale Sayers
Pro Football Hall of Fame member Gale Sayers is honored at halftime during the game between the Minnesota Vikings and the Chicago Bears at Soldier Field on October 31, 2016 in Chicago, Illinois. Stacy Revere/Getty Images