The Kryptonian Dev-Em is a troubled juvenile delinquent, unable to quench his rebellious attitude and obey the laws of Krypton. However Dev-Em was one of the few who believed in the words that the scientist Jor-El warned of, Krypton's impending destruction. Dev-Em than placed himself and his parents in suspended animation in an orbiting space capsule. When Krypton exploded, Dev-Em's ship was blasted into space, eventually landing on Earth. Dev-Em tracks down Krypton's only other survivor, Jor-El's son SuperBoy. He battles and imprisons SuperBoy in the Phantom Zone, quickly assuming his identity in an effort to destroy the Boy of Steel's life on his adopted world. However Dev-Em has a change of heart and releases SuperBoy and departs from the twentieth century, traveling through time to finally settle on the more advanced Earth of the 30th century. Since no one in Smallville will believe SuperBoy's story of the impostor, he develops a cover story that he was acting under the influence of Red-Kryptonite and restores his reputation.
Dev-Em returns and it is revealed that the so-called "Knave of Krypton" has reformed and joined the Interstellar Counter-Intelligence Corps of the 30th century. He works side by side with Mon-El and meets the rest of his teammates,the immanent super team of the 30th century the Legion of Superheroes . He was offered membership by Mon-El, after he talked the rest or the members into it, Dev-Em rebuffed the invitation. Despite his occasionally abrasive nature, Dev-Em aids the Legion on several occasions including battling the Dark Circle's terrorism attempts, challenging new cadets of the Legend Academy, and most notably in the " Great Darkness Saga" against the enigmatic Darkseid,where he battles his Daxamite army, almost falling until his timely rescue by the Heroes of Lallor.
With the current continuum was rewritten, Dev-Em's Post-Crisis background was also changed. Due to Kryptonians no longer existing in the wake of the Man of Steel's history being altered , his entry in the Who's Who in the Legion of Superheroes encyclopedia-like series says that he is David Emery. A native to the home world of the Legionnaire Saturn-Girl who uses his mental powers to give himself Kryptonian super powers. However the stories in this series are not involved in the current continuum.
Dev-Em later appears in the " Time and Time Again" storyline in which SuperMan goes between the 30th century and the 20th century. Superman soon encounters Dev-Em, now portrayed as an out of control insane Daxamite , now an adult whose powers rivaled Superman's. He tried to destroy the Earth's orbiting moon but was challenged by that alternate future's incarnation of the Legion. Dev-Em makes short work of Superman, his descendant Laurel Grand and the rest of the Legion. Dev-Em is seemingly stopped by the cunning Shrinking Violet as she shrinks to a tiny size and enters Dev-Em's ear, scratching his inner ear. However, he soon initiates the alien invaders the Dominators secret Triple Strike program, destroying the moon and causing massive damage to cities across the Earth.
Post-Infinite Crisis History
During the tremendous aftermath of the Infinite Crisis, Kon-El had died and a mysterious man calling himself Devem was a member of a group of zealots, the Cult of Kryptonians in the 52 series. Shown to be an escapee from a psych ward named Derek Mathers, who had been caught for fraud in the past.
Having his story re-written yet again Dev-Em soon appears as a renegade Kryptonian criminal, imprisoned into the Phantom Zone Dev-Em continues his murderous behavior even within the Zone. With the aid of Mon-El, Superman battles and beats him allowing Mon-El to transport him into the 30th Century.