Chicago Bears icon Dick Butkus, revered as one of the most ferocious tacklers in NFL history, died Thursday in California at the age of 80, his family said.

Butkus, who played in eight Pro Bowls and was twice named NFL Defensive Player of the Year, passed away peacefully in his sleep at his home in Malibu, his family said in a statement.

Bears chairman George H. McCaskey later paid tribute to Butkus as "the ultimate Bear, and one of the greatest players in NFL history."

"He was Chicago's son," McCaskey said in a statement. "He exuded what our great city is about … He refused to accept anything less than the best from himself or his team-mates."

Born in Chicago in 1942, Butkus excelled as a high school gridiron player before forging a successful college career at the University of Illinois.

He was selected with the third overall pick of the 1965 draft by the Bears, where he would remain for the entirety of his NFL career before a knee injury forced his retirement in 1974.

Despite playing on a struggling Chicago team — the Bears never reached the playoffs during Butkus's playing days — the 6ft 3in linebacker was regarded as one of the best players in the NFL.

At the heart of Butkus's reputation was his ferocity, with the NFL Network in 2009 naming him one of the most feared tacklers in the history of the sport.

Sometimes his hard-nosed approach would stray into murky territory, with allegations of intimidatory tactics that crossed the line, including biting offensive players.

That persona earned him a litany of nicknames — The Enforcer, the Animal, the Maestro of Mayhem and Robot of Destruction.

"I just loved the game, and I thought that's the way to play it," Butkus said in an interview years after his retirement.

Often, Butkus would imagine insults by opponents in an effort to motivate himself.

"When I went out on the field to warm up, I would manufacture things to make me mad," Butkus once said.

"If someone on the other team was laughing, I'd pretend he was laughing at me or the Bears. I'd find something to get mad about. It always worked for me."

The effect on opponents was often chilling.

"If I had a choice, I'd sooner go one-on-one with a grizzly bear," former Green Bay Packers running back MacArthur Lane once told an interviewer when asked about Butkus.

"I prayed that I could get up every time Butkus hit me."

Butkus's fellow Hall of Famer Deacon Jones famously remarked: "Every time he hit you, he tried to put you in the cemetery, not the hospital."

But Bears chairman McCaskey said Butkus's tough-tackling persona masked a softer side.

"Dick had a gruff manner, and maybe that kept some people from approaching him, but he actually had a soft side," McCaskey said, paying tribute to Butkus's philanthropic post-career work in campaigning against performance-enhancing drugs and promoting heart health.