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American football legend Gale Sayers has died of natural causes. He was 77.

The Chicago Bears star and Hall of Fame running back was nicknamed "Kansas Comet" for his electrifying speed. Sayers played his entire NFL career - 6 years - with the Bears.

Sayers set an NFL record in his first season as a professional by scoring 22 touchdowns, including six in a single game.

In 1967, Sayers and Bears teammate Brian Piccolo became the first interracial roommates in the NFL. Piccolo was later diagnosed with metastatic cancer and he passed away in 1970.

Sayers' and Piccolo's enduring friendship was documented in a made-for-TV movie, Brian's Song, with Sayers portrayed by Billy Dee Williams in the 1971 original and by Mekhi Phifer in the 2001 remake.

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In March 2017, Sayers' second wife, Ardythe Bullard, announced he had been diagnosed with dementia four years prior. She stated that a Mayo Clinic doctor confirmed his dementia was likely caused by physical contact during his brief football career.

"It wasn't so much getting hit in the head," she said. "It's just the shaking of the brain when they took him down with the force they play the game in."

Hall of Fame President & CEO David Baker said in a statement, "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. 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."