David Joiner is the identity created for Daniel Lamb by the Pickman Project following his mind-wipe. In order to prevent Leo from reentering Daniel's mind the Project erased his memories giving him a new personality free of the traumatic events of his past.
It is assumed, due to the mind-wipe, that David has no recollection of the numerous murders committed by his former self and its split personality. After killing Leo an amnesiac Daniel wakes up on a highway with no knowledge of who he is. He soon finds a package containing details of his new identity and home. With this discovery David Joiner is born.