Former Chicago Bears star Gale Sayers, considered one of the greatest running backs in the history of the National Football League despite a career cut short by knee injuries, has died at age 77 after living with dementia.

Known as the "Kansas Comet," Sayers was voted into the Pro Football Hall of Fame in 1977 despite playing just seven seasons, all with the Bears. At 34, he was the youngest player ever inducted.

"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."

Commissioner Roger Goodell said in a statement, "The NFL family lost a true friend today with the passing of Gale Sayers. Gale was one of the finest men in NFL history and one of the game's most exciting players.

"Gale was an electrifying and elusive runner who thrilled fans every time he touched the ball. He earned his place as a first-ballot Hall of Famer. We will also forever remember Gale for his inspiration and kindness. Gale's quiet unassuming demeanor belied his determination, competitiveness and compassion."

Sayers was a five-time All-Pro who averaged 5 yards per carry for his career and twice led the league in rushing, including in 1969 (1,032 yards) after having torn the ACL and MCL in his right knee late in the previous season.

A major injury to his left knee in 1970 was too much for him to overcome, and he retired in 1971.

His career numbers of 4,956 yards and 39 touchdowns on the ground came primarily over five seasons, as he played sparingly in 1970 and '71.

As a returner, Sayers was also devastating, scoring six touchdowns and averaging more than 30 yards per kickoff return, with two touchdowns and 14.5 yards per punt return.

Legendary Bears coach George Halas, as he presented Sayers for his Hall induction, said, "If you want to see perfection as a running back, you best get ahold of a film of Gale Sayers. He was poetry in motion. His like will never be seen again."

Sayers was born in Wichita, Kansas, and was an All-American at Kansas. He was a first-round pick of Bears in 1965 and once scored six touchdowns in a game.

For his bounce-back season in 1969, he was awarded the NFL Comeback Player of the Year Award, which he promptly passed on to close friend and teammate Brian Piccolo, who was dying of cancer. Their relationship was detailed in Sayers' autobiography "I Am Third" and the TV movie "Brian's Song."

Sayers was named to the NFL's 75th Anniversary Team in 1994 at halfback and kick returner, the only player named at two positions.

Sayers' family earlier this year discussed his experience with dementia.

Roger Sayers, his brother, told the Kansas City Star in a phone interview that it's "tough to build memories all your life, and the next thing you know, you don't remember anything."