Gale Sayers, who became a Hall of Fame football star as an electrifying running back for the Chicago Bears and found wider fame through “Brian’s Song,” a poignant television movie that chronicled his friendship with a cancer-stricken teammate, died Sept. 23. He was 77.

His death was announced by the Pro Football Hall of Fame, which did not say where or how he died. His wife, Ardythe, revealed in 2017 that Mr. Sayers had dementia, a diagnosis that she attributed in part to his playing career.

Mr. Sayers, a Wichita native who became known as “the Kansas Comet,” left an indelible mark on the National Football League despite injuries that limited him to 68 games. Few running backs were as dynamic in the open field or could match his ability to wriggle away from defenders, hurdle opponents and sprint effortlessly into the end zone.

“Just give me 18 inches of daylight,” he once said. “That’s all I need.”

Although Mr. Sayers was relatively small for a pro halfback, at 6 feet and 200 pounds, he was ultimately ranked among the heavyweights, mentioned in the same breath as legends such as Jim Brown and Walter Payton. He was also unusually versatile, a sure-handed receiver, master return artist and capable passer who could surprise defenses with a left-handed toss downfield.

“He was the best runner with a football under his arm I’ve ever seen,” Mike Ditka, who played with Mr. Sayers and later coached Payton, told Sports Illustrated in 2010. Another former teammate, Hall of Fame linebacker Dick Butkus, told the magazine: “He had this ability to go full speed, cut and then go full speed again right away. I saw it every day in practice. We played live, and you could never get a clean shot on Gale. Never.”

Mr. Sayers was a two-time all-American at the University of Kansas before being drafted by the Bears in late 1964. He went on to set records in his rookie season, gaining 2,272 all-purpose yards as a runner, receiver and kick returner and scoring 22 touchdowns. Six came on a muddy field against the San Francisco 49ers, when he tied a single-game record that still stands.

Only Ernie Nevers, in 1929, and Dub Jones, in 1951, had scored six touchdowns in an NFL game. Mr. Sayers scored on an 80-yard screen pass, rushed for four touchdowns and returned a punt 85 yards in the rain for his sixth. “I can still see the 49ers sloshing around in the mud,” he told the Los Angeles Times two decades later. “It seemed like everyone was slipping but me.”

Mr. Sayers was named a first-team all-pro in each of his first five seasons, led the NFL in rushing in 1966 and 1969 and became the youngest player inducted into the Hall of Fame, at age 34 in 1977. By then, knee injuries had led him to retire after seven seasons, including several in which he was variously replaced and joined in the backfield by Brian Piccolo, a former free agent from Wake Forest University.

The men formed an unusual duo. Mr. Sayers was Black and soft-spoken, Piccolo was White and gregarious. When they were paired together on road trips in the late 1960s, they became the first interracial roommates in NFL history, according to the Pro Football Hall of Fame, and forged a high-profile friendship in the midst of the civil rights movement.

When a sportswriter asked what they talked about on the road, Piccolo joked, “Nothing but the normal racist stuff.” Mr. Sayers was later asked whom he would prefer as a roommate if he had a choice. “If you’re asking me what White Italian fullback from Wake Forest, I’d have to say Pick,” he said.

Their bond strengthened in 1969, when Piccolo began to show signs of fatigue, later diagnosed as cancer. The nature of his illness was not widely known until the next year, when Mr. Sayers referred to the disease while accepting an NFL award for courage. He had led the league with 1,032 rushing yards after undergoing a difficult rehabilitation program, encouraged by Piccolo, for torn ligaments in his right knee.

“You flatter me by giving me this award, but I tell you here and now that I accept it for Brian Piccolo,” Mr. Sayers said in his acceptance speech. “Brian Piccolo is the man of courage who should receive the George S. Halas Award. . . . I love Brian Piccolo, and I’d like all of you to love him, too. Tonight, when you hit your knees, please ask God to love him.”

Three weeks later, on June 16, 1970, Piccolo died at age 26.

Mr. Sayers wrote about their friendship in a chapter of “I Am Third,” a memoir published later that year with journalist Al Silverman. Named after a motto Mr. Sayers took from his college track coach — “The Lord is first, my friends are second and I am third” — the book became better known after it was excerpted in Look magazine and inspired the ABC movie “Brian’s Song” in 1971.

Starring James Caan as Piccolo and Billy Dee Williams as Mr. Sayers, the movie won five Emmy Awards, drew the admiration of President Richard M. Nixon (“Believe me, it was one of the great motion pictures I have seen”) and was screened in high school and college classrooms for decades. It was remade as a TV movie in 2001.

“It’s the first bro romance on film,” actress Judy Pace, who played Mr. Sayers’s wife, Linda, in the original movie, told the Undefeated in 2016. “It was the first time that men actually cried in front of other people. It may have been the first time that kids ever saw their fathers cry.”

The movie came out after Mr. Sayers suffered ligament damage in his left knee, which never felt right again. He retired in September 1972, at age 29, and later told Sports Illustrated that more people approached him to talk about “Brian’s Song” than about his football career.

“That’s fine,” he said. “I’ll never, ever forget Brian. That part of my life will be with me forever.”

But for those who saw Mr. Sayers play — or pored over grainy film clips showing him slip between tacklers, leap over defenders, plant his heel and suddenly switch directions mid-sprint — his runs were no less memorable. Reporters would ask how he pulled off a particular play, but Mr. Sayers always offered the same explanation.

It was simply a gift.

“When I’m carrying the ball there isn’t any play going through my mind,” he told Sports Illustrated in 1966. “When I come to a tackler I don’t think, ‘Now fake one way and cut the other.’ My feet just go. I don’t think about it at all. I just do it, and I don’t really know how. Where my feet go, I go.”

Gale Eugene Sayers was born in Wichita on May 30, 1943. His father was a mechanic and car polisher, his mother a homemaker, and the family moved to Omaha when Gale was 8 or 9, giving him a chance to play in an organized football league for the first time.

Mr. Sayers also starred in track, setting a state long-jump record of 24 feet, 101/2 inches that stood for 44 years, according to the Omaha World-Herald. In his telling, he also gained 50 pounds the summer before his sophomore year, after weighing 110 as a freshman. Pushing a lawn mower had apparently helped, he said.

After averaging 6.5 yards per carry in college, Mr. Sayers left school early and was the fourth overall pick in the NFL draft. He was selected just after Butkus, but despite picking two future Hall of Famers the Bears had an aging roster under head coach George Halas and never made the playoffs with Mr. Sayers on the team.

Mr. Sayers’s career average of five yards a carry still ranks among the NFL’s top 10, and his career average of 30.56 yards per kickoff returns remains the best in league history. He was named the best running back of the NFL’s first 50 years and was selected last year to the league’s 100th-anniversary “all-time team.”

His marriage to Linda McNeil ended in divorce, and in 1973 he married Ardythe Bullard. They settled in Wakarusa, Ind., and supported organizations including the Cradle, a Chicago-area adoption agency that launched the Ardythe and Gale Sayers Center for African American Adoption in 1999.

Mr. Sayers had six children, but complete information on survivors was not immediately available. His older brother, Roger, starred in track, and a younger brother, Ron, played eight games as a running back for the San Diego Chargers.

After retiring from the NFL, Mr. Sayers returned to the University of Kansas as an assistant athletic director and student. He completed his bachelor’s degree in physical education in 1975 and received a master’s degree in educational administration in 1977.

He later became athletic director at Southern Illinois University at Carbondale and founded a technology consulting firm after failing to win an NFL front-office job in the early 1980s. Mr. Sayers said he wrote to every team in the league and received only one reply, in the form of a rejection letter.

He attributed the lackluster response to racial prejudice — the NFL’s first Black general manager, Ozzie Newsome, was hired only in 2002 — and went on to devote himself to philanthropy and business. Ernst & Young named him an Entrepreneur of the Year in 1999.

Mr. Sayers said he had looked ahead to a business career for decades, having joined the NFL long before television exposure and marketing deals helped drive star athletes’ earnings into the millions of dollars. He had worked at the brokerage firm PaineWebber while still playing for the Bears, going into the office when he was not at practice, including the day after his six-touchdown game.

“As I prepared to play, I prepared to quit,” he said. “I walked away, and I never looked back.”

Matt Schudel contributed to this report