Background: William Miller Edwards (June 21, 1905 - June 12, 1987) was an American football player and coach. He served as the head football coach at Western Reserve University, Vanderbilt University and Wittenberg University in a career lasting more than 30 years, compiling a win-loss-tie record of 168-45-8. Edwards also coached the Detroit Lions of the National Football League (NFL) from 1941 to 1942, tallying a 4-9-1 record, and served as an assistant coach for the NFL's Cleveland Browns in the late 1940s. Raised near Massillon, Ohio, Edwards was the son of an immigrant from Wales who worked in the area's coal mines.
Context: Edwards resigned from coaching in 1969, when he was 63 years old, although he continued to work at Wittenberg as the school's athletic director. Dave Maurer, his long-time assistant, took over as the school's coach. By the end of his career, Edwards's 168-45-8 overall college record gave him the second-best winning percentage in the country among active coaches with at least 100 wins. Edwards was given a commendation by President Richard Nixon for his achievements as a coach and won a Football Writers Association of America award for contributions to the game. "His retirement is Wittenberg's loss, but more than that, it is college football's loss," University of Alabama coach Bear Bryant said at the time.  Edwards retired in February 1973 after 39 years as a coach and administrator and said he would concentrate on hunting and fishing. He was inducted into the Ohio Football Coaches Association Hall of Fame in 1979, Wittenberg's Athletics Hall of Honor in 1985 and into the College Football Hall of Fame in 1986. He was also inducted into the Western Reserve Hall of Fame and the Vanderbilt Hall of Fame in 1986. Edwards died in 1987. He and his wife Dorothy had three children.  The tough but compassionate approach to coaching Edwards espoused influenced many men who worked under him, including Maurer, who led Wittenberg to a 129-23-3 record between 1969 and 1983. Wittenberg's football stadium is named Edwards-Maurer Field in honor of both head coaches. The winner of the Wittenberg-Case Western Reserve football game receives the Bill Edwards Trophy.  Edwards was also close with Steve Belichick, who played for him at Western Reserve and for the Detroit Lions and later served as an assistant under him at Vanderbilt and North Carolina. Belichick's son Bill was named after Edwards, who was also Bill's godfather. Bill Belichick later became an assistant coach in the NFL and is the head coach of the New England Patriots as of 2018. At what is now known as Case Western Reserve University, the football stadium, DiSanto Field, hosts its distinguished guests inside the Coach Bill Edwards President's Suite.
Question: what did he die of?. Whats the answer?