L is for... Lazarus

 

The elderly Professor Lazarus was a scientist who was working on a genetic manipulation device which was designed to rejuvenate people. He had a number of wealthy backers, such as Lady Thaw and the politician Harold Saxon. His personal assistant was Tish Jones - sister of the Doctor's companion Martha. Through her the Doctor and Martha got an invite to Lazarus' unveiling of his machine. He elected to test it on himself. The process went awry and the Doctor had to step in and stop it. When he emerged, Lazarus was now a young man.

Suspicious, the Doctor obtained a sample of his DNA. It transpired that Lazarus had activated long-dormant genes which would cause him to mutate. The scientist attempted to woo Tish, but he started to transform into a huge, scorpion-like creature, exhibiting several discarded genetic traits. He killed Lady Thaw and some of the other guests - sucking the life-force from them and leaving their bodies as desiccated husks.

When he trapped the Doctor and Martha in the machine, the former sabotaged it and Lazarus appeared to perish. However, he recovered and escaped. Tish pointed out nearby Southwark Cathedral, where Lazarus had said he sheltered from the Blitz during the Second World War. He was traced there. Unable to control the mutation, he transformed and chased Martha and Tish up to the bell tower. The Doctor boosted the organ, which reverberated in the bell tower and caused Lazarus to fall to his death.

He reverted to being an old man again.

Later, Saxon - really the Master - used Lazarus' genetic manipulation technology to create a weapon that was able to greatly age the Doctor.

Played by: Mark Gatiss. Appearances: The Lazarus Experiment (2007).

• With this episode, Gatiss became only the second person to have both written and appeared in Doctor Who stories - the first being Glyn Jones (writer of The Space Museum, who played Krans in The Sontaran Experiment).
• Gatiss would appear in the series on three further occasions - voicing a Spitfire pilot in Victory of the Daleks (which he also wrote), playing the Viking-like Gavrok in The Wedding of River Song, and also the Captain (who turns out to be the grandfather of the Brigadier) in Twice Upon A Time.
• To play the younger Lazarus, Gatiss supplied his own blond wig. It was the one he used to play the accident-prone vet in The League of Gentlemen - a character physically modelled on Peter Davison's Tristan Farnon in All Creatures Great and Small. He got a fee for loaning the wig to the production.