The NFL is mourning the loss of one of the best defensive players ever to grace the field as Dick Butkus died on Thursday in his sleep at his Malibu, California home.

As a middle linebacker who spent his entire career with the Chicago Bears from 1965-73, Butkus was a terror for opposing O-linemen as his speed and ferocious play on the field earned him the moniker of being “The Most Feared Man in the Game” according to a 1970 Sports Illustrated cover story.

With the Bears, he earned first-team All-Pro honors five times, was named to the Pro Bowl in eight of his nine NFL seasons, and was elected into the Pro Football Hall of Fame in 1979 on his first year of eligibility.

Bears chairman George McCaskey released a statement on the teams’ official Twitter handle regarding the sad news:

A moment of silence was held on Thursday Night Football before the Bears squared off with the Washington Commanders.

In an NFL career sadly cut short at 31 because of a knee injury, the third overall selection in the 1965 NFL Draft accomplished a lot in a short period, being named the Defensive Player of the Year on consecutive occasions in 1969 and 1970 even though his team never made the playoffs in his pro career.

The Chicago-born product played his college ball at the University of Illinois, where he was a Unanimous All-American in 1963 and a Consensus All-American the following year while also being named the MVP of the Big Ten in 63.

Butkus inherited the role of middle linebacker on the Bears from Hall of Famer Bill George, who popularized the position when he abandoned his three-point stance in the middle of the defensive line and started each play several paces away, something which allowed him to watch plays unfold before racing to the ball.

Throughout his professional career, Butkus had speed, strength, and agility that many could only dream about, picking off five passes, recovering six fumbles, while forcing another six in his rookie NFL campaign as his reputation as a disruptor extended well past his ability to create takeaways.

Once described by Playboy magazine as “the meanest, angriest, toughest, dirtiest” player in the league, Butkus became an instant celebrity after leaving the game, appearing in numerous movies and TV shows upon retiring, such as “Brian’s Song” which is based on the friendship of two of his Bears teammates Gale Sayers and Brian Piccolo.

His charity, the Dick Butkus Foundation, was established at a Southern California hospital to encourage early screenings to detect heart disease, while that foundation also oversees the Butkus Award, which began in 1985 to honor the best linebacker in college football.

He was briefly head coach of the XFL’s Chicago Enforcers but was replaced by Ron Meyer during the league’s only season in 2001.

Butkus was named to the NFL All-Decade Team in the 1960s and 70s while later having his iconic number 51 retired by the Bears, and he was elected as one of the top 100 players in the franchise’s history.

He is survived by his wife Helen and children Ricky, Matt, and Nikki, while his nephew Luke has previously coached in college and had a brief tenure with the Bears.