History
When Apocalypse started his plans for world domination, he captured four people who he saw as being good enough to be his Horsemen and corrupted them. Spider-Man became Pestilence, Blob became Famine, Archangel became Death, and Cable became War.[1]
Pestilence, Famine, and Death encountered Deadpool, Cannonball, and Siryn during their alternate reality search for their reality's Cable. They fought the Horsemen and defeated them.[1]
However, they then encountered and fought War, who easily defeating them. Realizing that he could not defeat him, Deadpool body-slided away, followed by Cannonball and Siryn three minutes later.[2]