NFL legend Dick Butkus -- one of the greatest linebackers of all time -- has died, TMZ Sports has learned. He was 80 years old.
Our sources tell us ... paramedics responded to a call for a medical emergency at Butkus' residence in Malibu at 12:51 PM. He was pronounced dead at the scene.
We're told someone went to check on Butkus at his home on Thursday ... and he was found unresponsive.
Butkus is among the most intimidating players to ever step onto a football field -- coming in at 6'3", 245 pounds, he was a defensive standout at the University of Illinois before joining his hometown Chicago Bears in 1965 .