Private Steve Gray was a UNIT soldier.
During Operation Blue Sky he and Private Harris investigated the basement of an ATMOS factory, where they found a cloning pool. Gray showed a great deal of fear and overreaction to what Harris identified as a human embryo that was harmless, for which General Staal declared him an unfit soldier, before the two of them were hypnotised. He was later used to teleport the TARDIS to the Sontarans' ship, and he was killed by a Sontaran soldier alongside Harris after the pair had completed their objectives. (TV: The Sontaran Stratagem/The Poison Sky)