If we're sticking to Iconic, rather that influential or most significant, then may I be so bold as to suggest that it wasn't so much an individual but rather a group; all those non-British, non-Commonwealth, individuals from nations not engaged in the conflict who fought because they believed that cause was just (the same goes equally for those who joined the various arms of all Allied forces).
IMHO, the symbolism of their efforts and sacrifice; not fighting for a god, a king or a country, but rather out of a sense of right and wrong, transcends that of the eminent names suggested.
JAS