Once a simple Kansas farm boy, Joshua Walker wanted nothing more than to make his parents proud and serve his country. Knowing service meant sacrifice, Walker volunteered for Amanda Waller's "Last Line" experimental program. Using Kryptonite as a bonding agent, Joshua's DNA was intertwined with Doomsday's, mutating him into an unstoppable monster. Dubbed the "All-American Boy," Walker's sole purpose became subduing Superman, and if necessary, kill the Man of Steel.