Native to the planet Ria, the Kronans are a highly-advanced race who developed space-travel technology thousands of years ago (shortly after creating the Gravitron, a device installed upon all Kronan starships that enable them to defy the laws of gravity). Having achieved space-travel capability, the Kronans soon set out to conquer other worlds, using their giant Mechano-class and Mekkanoid-class robot drones to subjugate less advanced civilizations. Approximately 5,000 years ago, the Kronans attempted an invasion of Earth. Landing in the city-state of Babylon in a region designated Mesopotamia, the Kronan invasion force was confronted by King Gilgamesh, ruler of the nearby city-state of Uruk. Gilgamesh, with the assistance of a time-traveling warrior from Earth’s future named Captain America, forced the ill-prepared Kronans to retreat to their starship and leave Earth.
After having millennia to contemplate the tactical errors made in their first Earth invasion, the Kronans staged another attempted invasion of the planet approximately 10 Earth years ago. Staging an attack from a secret base on Iapetus, a moon orbiting the nearby planet of Saturn, the Kronans landed a much larger invasion force in the nation of Norway on Earth’s Scandinavian Peninsula. The brothers Korg and Margus, still inexperienced young bricks at the time, were among the Kronans assembled for the attack. Anxious to conquer, the invasion force pursued a native bystander, Dr. Donald Blake, into a nearby cave where he uncovered Mjolnir, the hammer of Thor, one of Earth’s various thunder gods. Meanwhile, the Kronans proceded to attack Earth’s military forces, using their illusion-casting technology to scare them into retreat. Eventually Blake, who had been transformed into Thor by the Mjolnir’s magic properties, confronted the Kronans and used his godly powers to defend against every attack the invaders initiated. Finally, the Kronans unleashed one of their Mechano-Monster units against the god, but Thor destroyed it with one swing of Mjolnir. Badly beaten and terrified at Thor’s power levels, the Kronan invasion force once again fled to their starships and retreated, only to learn much later that not all Earth natives possessed Thor’s godly powers.
In their hasty retreat, one of the Kronan starships crashed on an asteroid and became separated from the rest of the fleet. When Thor and a group of his fellow Earth gods happened upon the asteroid, the Kronans attacked in an attempt to steal the starship of the gods. Unable to match the power of the gods, the Kronans salvaged the Gravitron from their disabled vessel and modified it into a weapon to counter Thor. But Thor once again prevailed over the Kronans, destroying the vessel and setting off a chain reaction that destroyed the entire asteroid.
Sometime during his travels, Korg and his brother Margus were captured by the Sakaar Empire and implanted with obedience slugs to ensure their loyalty. Korg was one of the survivors of the Maw Gladiator Training School, and was paired with the Hulk and several others in a gladiator team. In their first battle, the Hulk forced Korg to kill Margus, who had been driven insane. Korg was anguished, but got over his brother's death and eventually developed a friendship with the Hulk. Korg was freed by the Silver Surfer after fighting in the Imperial Arena in a bid for the Emperor's favor.