Private Steve Gray was a UNIT soldier. His call sign was Greyhound Sixteen.
During Operation Blue Sky in 2009, 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. (TV: The Sontaran Stratagem) 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 Poison Sky)