What title identified Douglas MacArthur as the Allied occupation leader in Japan after its 1945 surrender?

The title identifying Douglas MacArthur as the Allied occupation leader in Japan was Supreme Commander for the Allied Powers.

The title is usually abbreviated SCAP. MacArthur held it from the beginning of the occupation in 1945 until April 1951, when President Harry Truman relieved him during the Korean War.

SCAP was both a person and the name commonly used for the occupation headquarters and its administrative apparatus. The organization supervised Japan’s demilitarization and helped direct political, legal, educational, and economic reforms.

SCAP did not mean that Japan ceased to have every domestic institution. The Japanese government continued operating under Allied supervision, while the emperor remained on the throne but renounced his status as a divine ruler in the postwar settlement.