Oscar Frederick Heidenstam (27 February 1911 – 21 March 1991) was a Cyprus-born British bodybuilding champion and physical culturist.

He had a passion for sport from a very young age, and throughout his school years he participated in track and field athletics, gymnastics, hand balancing, swimming, diving, water polo, tennis, squash, rackets, hockey, football, and rugby.

At the age of 18 he won thirty medals and two silver cups for his achievements in various sports including rugby, track and field athletics, and gymnastics.

Heidenstam served in the British armed forces during the Second World War, and by the time he left the military in 1948 he had attained the rank of Major.

During the war he was a physical training instructor with the Army Physical Training Corps (APTC), as well as being involved in action in Palestine (Israel), Egypt, Tunisia, Sudan, Yugoslavia and Turkey.