Adrian Carton de Wiart
Every time someone is described as being unkillable, you can be sure there is a compelling justification. Adrian Carton de Wiart experienced this. De Wiart served in the Boer War, the First World War, and the Second World War with just one eye and one hand. For his troubles, he received gunshot wounds to the ear, hip, leg, ankle, and through the skull, as well as the face, leg, and hip. He made it through everything.
Eight times during the First World War alone, de Wiart suffered serious injuries. He had been shot in the stomach and groin during his time fighting in the Boer War. He carried grenades in his one remaining functional hand while using his teeth to remove the pins when he had no other options. The doctor refused to amputate his fingers because an artillery barrage had destroyed the appendage, so he tore them off himself.
He was shot down over the Mediterranean during the Second World War. He swam to shore, where the Italians caught him. He was in his sixties at the time, and despite being old, one-handed, and blind in one eye, he often managed to escape his POW camp. He represented Winston Churchill personally in China after the war, and he passed away quietly at the age of 83.