Arnauld Klimt was a scientist.
He conducted illegal weapons research for Falsh Industries on Carme. He created the space slugs and Halcytone. When he learned the moon was going to be destroyed to cover up the research, he launched his laboratory into space to escape. To conceal his identity, he faked his own death, then killed Chief Supervisor Torvin and assumed his identity.
Drug use was legal at this time, and Klimt took a variety of narcotics. He used wake-up pills to counteract the diamorphine he was taking. Unfortunately, when Trix found the pills on what she thought was Klimt's body, the Eighth Doctor threw them away and replaced them with aspirin. Klimt stole the pills from Trix later, not realising the substitution. Eventually Klimt became totally unhinged. He tried to kill the Doctor, who was forced to cause Klimt's death to save himself. (PROSE: To the Slaughter)