Tom Nellis was a male Human Starfleet officer in the 23rd century. He served in the operations division aboard the Antares, under the command of Captain Ramart. Nellis was the ship's first officer and navigator.
In 2266, the Antares transferred a young man, Charles Evans, who had been stranded on the planet Thasus for seventeen years, to the USS Enterprise, so he could be transported to Colony 5 where he would be reunited with his closest living relatives. While Charlie was on board the Antares, however, the crew discovered that he had incredible psychokinetic powers, and could force the crew to do whatever he wanted.
After transferring Charlie to the Enterprise, Ramart attempted to signal them to warn them of the danger that Charlie posed, but Charlie used his powers to remove a warped baffle plate from the Antares's energy pile, causing a warp core breach which destroyed the ship with all hands lost. (TOS: "Charlie X")