Muhammad Ali, born Cassius Clay (January 17, 1942 – June 3, 2016), was a professional boxer and activist. He is widely regarded as one of the most significant and celebrated sports figures of the 20th century. At age 18, he won an Olympic gold medal; at age 22 he won the WBA, WBC, and lineal heavyweight titles from Sonny Liston in an upset victory. Clay converted to Islam and became involved in the Civil Rights Movement. In 1966, he refused to be drafted into the military, citing his religious beliefs and opposition to the Vietnam War. Ali is regarded as one of the leading heavyweight boxers of the 20th century. He remains the only three-time lineal heavyweight champion, having won the title in 1964, 1974, and 1978. After retiring from boxing in 1981, Ali devoted his life to religious and charitable work.