Lee Kelso was a Starfleet officer who served as navigator aboard the USS Enterprise in 2265. Among his friends aboard ship was helmsman Gary Mitchell, whom Kelso referred to as "Mitch".
Kelso was on duty when the Enterprise encountered the barrier at the edge of the galaxy, during its mission to probe out of the Milky Way. Upon encountering the barrier, the Enterprise sustained serious damage to her warp engines, and Mitchell was affected in such a way that he began to develop extraordinary psychic abilities. Kelso visited Mitchell in sickbay, who informed Kelso that the ship's starboard impulse pack was burned out. As there was seemingly no way Mitchell could have known this, Kelso initially assumed that Mitchell was joking. Mitchell insisted, however, prompting Kelso to double-check the impulse pack, confirming that Mitchell's report was accurate.
In an attempt to repair their warp engines, the Enterprise traveled to Delta Vega, in the hopes that they could adapt some of the power packs from the automated lithium cracking station on the surface. Kelso was put in charge of the operation, and was able to successfully repair the engines. During the repair process, Captain Kirk ordered Kelso to rig a self-destruct switch that would destroy the entire station, should Mitchell, whom Kirk was planning to strand on the surface due to his increasing instability, escape his captivity from the station's brig. In order to stop him, Mitchell telekinetically strangled Kelso to death with a cable.