Gregson Grenville was a security guard in Deimos Moonbase.
Gregson was taught in school that the Ice Warriors "were all melted when the invasion fleet spiralled into the sun", "hundreds of years" before his time.
Gregson was the husband, later ex-husband, of Mrs Grenville, though he later said, "I never did get over her."
When Professor Schooner escorted the Eighth Doctor and Tamsin Drew to Gregson for trespassing, Gregson said he could do nothing about it until the next passenger rocket left for Mars. Gregson then picked up a distress call from a tourist shuttle, which the Doctor proved was a genuine Ice Warrior threat using the infra-red scanners.
When the Doctor appeared to have died in the middle of negotiations with the Ice Warriors, Supervisor Finch ordered Gregson to activate the atmospheric re-ioniser and fry the tourist shuttle the Ice Warriors were on. This failed when Professor Schooner had sabotaged the emitters allowing the Ice Warriors to breach the base; Schooner having framed Tamsin for the act. Gregson imprisoned Tamsin.
While escorting Professor Schooner to the base's environment control suite, Schooner, instead of raising the temperature to slow down the Ice Warriors, lowered it so he could find out more about them, as Schooner believed them to have been "unique" and wanted to know more about them. Schooner shot Gregson in the leg, and told him to leave. The Doctor, upon discovering Gregson, helped free Tamsin and they tried taking him to the passenger rocket before it took off. However, Gregson didn't make it in time, and was killed by the rocket thrusters as it left Deimos. (AUDIO: Deimos)