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. Under Rojan's command, Tomar escaped with three other 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, Tomar was part of the boarding party that captured the USS Enterprise. Tomar oversaw the installation of Kelvan technology on the Enterprise, enabling them to return home and report their discoveries to the Kelvan Empire.
The humanoid sense perceptions and emotional tendencies were alien to Kelvan experience, leading Kirk and his senior officers to exploit Kelvan weaknesses. After Dr. McCoy showed him the pleasures of eating, Lt. Commander Montgomery Scott introduced Tomar to a drinking tour of the Milky Way. The two consumed copious amounts of alcohol until Tomar's twitchy body collapsed, soon followed by Scotty. Eventually, Kirk suggested that the Kelvan's new Humanity could be fully realized on a planet in the Milky Way, and the Kelvans restored control of the Enterprise. (TOS: "By Any Other Name")