Rex Clark (14 September 1935 — 19 October 1978) was an officer of the Australian Army and a collector of orders, decorations and medals as well as military history books and ephemera.

Major Rex Clark served as a member of the Australian Army Training Team in South Vietnam in 1963–1964.

In April 1964, during operation Lam Son 115, while one of two Australian observers with Vietnamese Rangers, they found themselves under fire from entrenched Viet Cong around their helicopter landing zone.

[4] The Dhofar Rebellion in Oman that raged between 1962 and 1976 attracted foreign mercenaries to help fight the Marxist guerrillas who were threatening the regime of the British-educated Sultan Qaboos bin Said al-Said.

This war attracted soldiers with combat experience, who were recruited into battlefield leadership roles to shore up the Sultan's regime and to help prevent the key oil-exporting Strait of Hormuz from falling under communist control.

Clark infuriated the Australian Defence Forces by joining the army of pre-revolutionary Iran, an Omani ally, while on leave in 1975.

[18] Following an investigation in the disappearance of rare military relics and medals from collections and museums around the world, in 1978 Australian Commonwealth Police discovered duplicate military medals in Sydney and also recovered the original tunics of Sir John Monash and Sir Thomas Blamey, stolen from the Australian War Memorial in Canberra.

[3][19] Clark was found dead with a self-inflicted gunshot wound to the head at his home in the Canberra suburb of Page, while still being under investigation.