Cao Văn Viên (December 21, 1921 – January 22, 2008) was one of only two South Vietnamese four-star army generals in the history of the Army of the Republic of Vietnam during the Vietnam War. He rose to the position of Chairman of the South Vietnamese Joint General Staff. Considered one of "the most gifted" of South Vietnam's military leaders, he was previously called an "absolute key figure" and one of "the most important Vietnamese military leaders" in the U.S.-led fighting during the Vietnam War. Along with Trần Thiện Khiêm he was one of only two four-star generals in the entire history of South Vietnam.