August 5, 1908 - December 17, 1967: Age 59
Harold Holt was an Australian politician who was elected Prime Minister in 1966. He had a long political career, but is remembered mostly for his support of Australian and American involvement in the Vietnam War (the Tony Blair of his day?), and for his mysterious disappearance.
He was an experienced swimmer and skindiver, but was suffering from health problems. He had collapsed the year before from "vitamin deficiency", leading some to suspect heart troubles, and was on strong painkillers for the flare-up of an old shoulder injury. On December 17 he went with friends to Cheviot Beach on the eastern arm of Port Phillip Bay, an area with heavy surf, strong currents, and dangerous rip tides. He insisted on plunging into the water despite warnings from his friends, and quickly disappeared from view. They raised the alarm immediately and for the next two days that area of the coast was combed in one of the largest search operations in Australian history. They never found him.
Rumours about his disappearance being faked abounded, with stories ranging from running away with a mistress, to being picked up by a Chinese submarine, to being abducted by a UFO. There were also rumours that it was suicide. The most likely explanation, however, is that Holt was caught in the strong undertow and carried out to sea, where he drowned.
Source: Wikipedia, Sydney Morning Herald