A "famous scientist" of Krypton who was sentence to twenty-five years in the Phantom Zone—for a crime he did not commit—by a Kryptonian "justice council" headed by Superman's father (see Jor-El), after the real perpatrator of the crime, who was himself never prosecuted, had hypnotized Quex-Ul into admitting his guilt and accepting his undeserved punishment.
Released from the Phantom Zone by Superman upon the expiration of his sentence in November 1962, Quex-Ul—who still views himself as a criminal and remains ignorant of his own innocence—acquires super-powers identical to Superman's in the atmosphere of Earth and immediately sets out to wreak vengeance on Superman for his father's role in his conviction by exposing Superman to the baleful radiations of gold Kryptonite, which would permanently strip Superman of his mighty super-powers.
Filled with remorse, however, when he learns that Superman has actually gone so far as to return through the time barrier to Krypton at the time the original crime was committed in order to prove Quex-Ul innocent of any wrongdoing, Quex-Ul hastily intervenes to prevent Superman from exposing himself to the gold kryptonite, but only at the cost of voluntarily exposing himself to the destructive radiations in Superman's stead. Stripped forever of his super-powers by the radiations of the gold kryptonite—and afflicted with "permanent amnesia" as the result of kryptonite damage to "some of his brain's memory cells"—Quex-Ul loses all recollection of his Kryptonian past and of his years in the Phantom Zone and, at the suggestion of Superman and with the cooperation of Perry White, is now employed in an ordinary workaday job in the production department of the Daily Planet (S No. 157/1: "The Super-Revenge of the Phantom Zone Prisoner!").