Lord Slaadek was an Ice Warrior that slept in the catacombs on Deimos after the "red dawn" destroyed Mars' environment, "many millions of years" before the 23rd century, according to the Eighth Doctor. (AUDIO: Deimos)
In the 23rd century, the Monk woke up Slaadek and eight other Ice Warriors in the catacombs to prevent Halcyon from becoming the Ice Warriors' new home planet a thousand years into the future. (AUDIO: The Resurrection of Mars)
Lord Slaadek and his Ice Warriors took over a tourist shuttle, holding several humans as hostages. The Eighth Doctor tried negotiating, but Slaadek ordered his death when Supervisor Finch said he was no use to the people of the base dead or alive. The Doctor survived thanks to the insulation of his suit.
The Ice Warriors quickly breached Deimos Moonbase so that they could use the atmospheric re-ioniser to terraform Mars into how it was long before, which would have caused the death of 600,000 human colonists. Professor Schooner showed Slaadek the re-ioniser, but realised that the Ice Warriors weren't as honourable or noble as he thought they were. He and the Doctor sabotaged the re-ioniser, while the Ice Warriors killed him while he bought some extra time for the Doctor. The base's staff and visitors were evacuated in a passenger rocket. (AUDIO: Deimos)
When the rocket returned to Deimos thanks to a gravity eddy, Lord Slaadek demanded to have the Doctor repair the re-ioniser. Slaadek tested the effects of the re-ioniser on the passenger rocket, killing all 600 people on board.
When the re-ioniser began its process on Mars, the Doctor, unable to reverse the effects, brought it "to a very sudden halt with a very loud bang" by reducing a critical feedback in the ionisation beam. At the last minute, the Doctor also made the process alter Mars into an Earth-like atmosphere rather than that of the Mars of long before. With only five minutes to escape to the catacombs, the Ice Warriors failed to make it when the feedback ignited the atmosphere of the moonbase. (AUDIO: The Resurrection of Mars)