Crozier was a bio-engineering scientist hired by the Mentors to perform life-saving surgery on Kiv on Thoros-Beta in 2379. In a fake version of events, he swapped Peri Brown's thoughts for Kiv's thoughts. This was later proved to be a fake, masterminded by the Valeyard. (TV: Mindwarp / The Ultimate Foe)

He had a daughter, Cordelia, who grew to hold a grudge against the Sixth Doctor. (AUDIO: Antidote to Oblivion)

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