William D. Leahy
On 20 July 1942, Fleet Admiral William D. Leahy became Chief of Staff to the Commander in Chief (20 July 1942 – 21 March 1949). He was not technically the chairman of the Joint Chiefs of Staff. Leahy's office was the precursor to the post of "Chairman of the Joint Chiefs of Staff". That post was established and first held by General of the Army Omar Bradley in 1949.