His ancestors were part of a wave of multi-generational starships dispatched to nearby galaxies to find new territories for the Empire to conquer and occupy. Reaching the Milky Way Galaxy after centuries in the intergalactic void, his ship was destroyed crossing the galactic barrier. Rojan escaped with four crew members in a life-craft to a Class M planet. The Kelvans adopted humanoid forms more compatible with the new region's intelligent life and available transportation.
After a false distress call attracted the attention of Captain James T. Kirk, Rojan's crew hijacked the USS Enterprise, and modified the vessel with Kelvan technology, so they could return home and report their discoveries to the Kelvan Empire. His mission was critical to the survival of the Kelvan species and civilization, and Rojan brooked no opposition. The Kelvan mission was to be completed by a commander who was his blood descendant. Except for one incident, where Kirk's escape attempt forced Rojan to demonstrate his dominance by distilling and killing Yeoman Leslie Thompson, Rojan was invariably polite and even-tempered with his captives.
The humanoid sense perceptions and emotional tendencies were alien to Kelvan experience. Coupled with social naiveté born from the relative isolation of a life spent in space and Rojan's courteous treatment of his opponent, Kirk and his senior officers exploited Kelvan weaknesses. Rojan was incited to a jealous rage by Kirk's seduction of Kelinda and the subtle needling of Spock. Kirk's suggestion that Rojan's Humanity could be fully realized in the Milky Way, and that a robotic envoy from the Federation could fulfill his mission in his place, was accepted, and Rojan returned control of the ship. (TOS: "By Any Other Name")