Second Doctor (clone)
From Tardis Wiki, the free Doctor Who reference
The Second Doctor was a clone created from the Fourth Doctor, however, he had came out as the Second. He had the Doctor's real memories, and indeed thought he was the Doctor. The Fourth Doctor met him and proved his false identity, but not before Hexford was moved into space, and the Shiscari infant nearly devoured him. The Fourth Doctor said that due to his cloning type, he would not live more than a few months. (AG: The Hexford Invasion, Survivors in Space)
