Complex sentence: John R. "Johnny" Cash (February 26,1932--September 12,2003) was an American singer-songwriter, actor, and author who was considered one of the most influential musicians of the 20th century.
Split into simpler sentences: John R. "Johnny" Cash (February 26,1932--September 12,2003) was an American singer-songwriter, actor, and author. He is considered to be one of the most influential musicians of the 20th century.