Nilson

Nilson was an officer on board Sea Base 4 in 2084 and Vorshak's second-in-command.

Nilson, along with Solow, was a convert to the ideology of the East Bloc, the power bloc opposed to the base. After the death of Solow's husband and parents, Nilson convinced her that the philosophy of the East Bloc was the answer to all of life's problems, but for the East Bloc to wipe out all suffering and injustice on Earth, sacrifices would have to be made. (PROSE: Warriors of the Deep)

Nilson used Maddox to commit sabotage on the base. After he was discovered by Vorshak, Nilson took Tegan Jovanka hostage. Nilson threatened to kill Tegan, but the Fifth Doctor blinded him with an ultraviolet converter. He stumbled down the corridor and was eventually shot and killed by the Sea Devils. (TV: Warriors of the Deep)

Behind the scenes
Peter Arne, Nicholas Ball, Tom Chadbon, Michael Gothard, Ian Holm, Dennis Lill, Ronald Lacey, Alfred Lynch, Ian McKellen, Clive Merrison, John Normington and Edward Peel were considered for the role before Ian McCulloch was cast.