Dick Butkus, the revered Chicago Bears linebacker, died last month as a result of a stroke, according to TMZ. The NFL hero passed away at his home in Malibu, California, on Oct. 5 at the age of 80. A death certificate issued by the Los Angeles Department of Health listed the immediate cause of death as “cerebrovascular accident,” TMZ reports, which is more commonly referred to as a stroke. The document also reportedly listed secondary causes including an irregular heartbeat in the weeks before Butkus’ death, years of high cholesterol, and atherosclerosis—a thickening or hardening of the arteries. The certificate also records that Butkus had coronary bypass surgery in 2001. Beginning in 1965, Butkus played nine seasons for the Bears over which he developed a fearsome reputation which earned him an induction into the Pro Football Hall of Fame in 1979.