Doomsboy was created when Bedlam tried to remove Superboy from existence by altering the past. To do so, he tampered with Project Cadmus' attempt to decipher Supermans Kryptonian DNA after he died. Because they could not clone Superman, Project Cadmus and Paul Westfeild ( a key player in Cadmus activities at the time) decided to clone Doomsday instead.
Eventually two clones were made. Doomsboy, the much smarter clone of Doomsday, and Conal (aka Superboy in this new reality) , the powerless clone of Superman. Westfeild raised Doomsboy as his son, while caring very little about Conal, who was considered Doomsboy's little Brother. Doomsboy was trained to take over the responsibilities of Superman, which he eventually did. And as the new man of steel, Doomsboy killed all his enemies and began to be known the world over as Earths new Superman. But Doomsboy secretly hated the Legacy he had adopted.
Doomsbiy eventually took a more criminal turn, taking what he called "tributes" from various companies for keeping them safe. Conal disapproved of these actions, suggesting that it wasn't a very Superman-like thing to do. This comparison infuriated Doomsboy, as he had begun to believe that Superman was judging him. Doomsboy made it clear that he could kill his weak "little brother" whenever he wanted.
After Superboy had stood up to his "brother", actions from the other members of Young Justice eventually freed Superboy from this alternate reality.
Doomsboy is much like Doomsday, except he exhibits sentience and human like intelligence. He has Super Strength, Stamina, and invulnerability comparable to Supermans.