Hanar was a Kelvan, member of an expedition from the Kelvan Empire in the radiation-imperiled Andromeda Galaxy.
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, Hanar escaped with three other crew members in a life craft to a 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, Hanar led the boarding party that captured the USS Enterprise so they could 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. Dr. McCoy subjected Hanar to repeated medical examinations, suggesting serious illness, and pumping him with stimulants. His mental state deteriorated until he angrily confronted Rojan, bursting with a litany of complaints. 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.