Years ago on Krypton, Gra-Mo is secretly the leader of a criminal gang. As leader of this gang, he uses fear and intimidation to control his subordinates, such as Ha-Kor, who he uses the threat of destroying his family should Ha-Kor betray Gra-Mo's secret society upon being captured by the authorities. For his crime of attempting to use a series of evil androids to prey on Kryptonian society under Gra-Mo's orders, Ha-Kor is sentenced to exile into outer space in a state suspended animation inside a specially-constructed space capsule, which is the standard method of criminal incarceration at this time before Jor-El's discovery of the Phantom Zone.
Soon after Ha-Kor's imprisonment, Gra-Mo is one of two candidates up for a seat on Krypton's ruling Science Council, the other being Jor-El. The two candidates are each to present a new invention to the council, with the winner of the contest being awarded the vacant seat on the council. Gra-Mo's invention is a new type of android servitor designed to replace the planet's robot work force since the android would not be subject to accidental mechanical interference, but unfortunately, Gra-Mo loses out on the seat on the council to Jor-El due to his android dissolving into a protoplasmic blob just after Jor-El had presented his invention of the Phantom Zone Projector.
Angered at his rejection by the council, Gra-Mo takes his revenge by using a telepathic control helmet of his own design to cause the robot police of Krypton to attack. Jor-El stops the revolt by magnetizing the planet's weather control satellite, drawing the police robots into the famed "Firefalls". Gra-Mo, however, is not exiled into the Phantom Zone upon being captured due to a temporary malfunction of the projector. Instead, Gra-Mo and his two henchmen are placed in suspended animation and exiled into orbit around the planet Krypton, becoming the last Kryptonian criminals to be sentenced to this form of punishment. When the planet Krypton explodes sometime later, the capsule carrying the sleeping Gra-Mo and his henchman is not destroyed, but is instead blasted into remote space. Years later, after the trio's capsule collides with a meteor in space that changes the ship's course trajectory, Gra-Mo and his subordinate's land on Earth.
By the time that Gra-Mo's capsule has arrived on Earth, many years have passed and the infant Kal-El has already grown into his teen years and become Superboy. Soon after their arrival and awakening on Earth, the trio is discovered by the Boy of Steel, who relates to them the tragic story of the end of Krypton. Pretending to be an old friend of Jor-El, Gra-Mo then hatches an ingenious plan to enact revenge upon Jor-El through his son. Secretly rebuilding his telepathic control helmet, Gra-Mo contacts the Phantom Zone exiles, who give him information to battle and defeat the teenage hero, with the promise that upon Superboy's defeat, Gra-Mo will use the projector to free the criminals from the zone. Though agreeing to the terms set forth by the spokesperson of the exiles, Jax-Ur, Gra-Mo actually has no intention of freeing the prisoners.
A few days later, Gra-Mo, disguised as a European gentleman known only as "Pater" arrives in Smallville with a boy named Reginald, who he states is his son. Reginald is actually a sophisticated lifelike android created by Gra-Mo and his henchmen who possesses immense superhuman strength, on par with that of Superboy. The "boy", after committing several acts of vandalism, fights Superboy, proving to the hero that he is just as strong as a Kryptonian, and, just after handing his glasses over to Johnathan Kent for safe keeping, goads the Boy of Steel into hitting him as hard as he can. Superboy complies with the request, and knocks the "boy" into the sky with one punch. The force of the punch disintegrates "Reggie", causing Superboy to believe he has taken the life of another being. After the "death" of "Reggie", Superboy vows to end his career as a hero, which plays right into Gra-Mo's hands.
With Superboy out of the way, Gra-Mo and his henchmen begin their conquest of Earth by robbing the Smallville National Bank. Gra-Mo and his cohorts are surprised by the sudden appearance of Superboy, who reveals he knows about Gra-Mo's subterfuge, telling the criminal that he figured that "Reggie" was an android when "...Jonathan Kent showed me "Reggie's" glasses! You slipped up, Gra-Mo! You made his glasses out of ordinary window glass! Therefore, I knew there was nothing wrong with "Reggie's" sight! Then, when I heard that a nearby chemical plant had been robbed of certain elements, I realized those elements could be used to make an android!"
A brief battle then ensues between Superboy and the three criminals, until he tricks them back into their space capsule with what appears to be the Phantom Zone Projector, but, however, the "projector" was in actuality a cardboard replica that Superboy had hidden there previously. While the three criminals are inside the capsule, Superboy seals it up and covers it in lead paint, which blocks out the rays of the yellow sun that grants a Kryptonian super powers, robbing the criminals of their abilities. With Gra-Mo and his henchmen now powerless, Superboy uses the real projector to banish them, ship and all, into the Phantom Zone, where Gra-Mo and his subordinates are berated for their incompetence by Jax-Ur (SB No. 104/1, Apr 1963: "The Untold Story of the Phantom Zone - Part I: The Crimes of Krypton's Master Villains"; SB No. 104/2, Apr 1963: "The Untold Story of the Phantom Zone - Part II: The Kid Who Knocked Out Superboy").
Gra-Mo is not seen again until he becomes involved in a scheme alongside a trio of himself, Jax-Ur, and Professor Vakox to use the shape-shifting abilities of Kryptonian juvenile delinquent and fellow Phantom Zone exile Cha-Mel to free them from the zone (SB No. 162, Jan 1970: "The Super-Phantom of Smallville!").