Richard Lazarus
Lazarus (also known as Dr. Lazarus or Professor Lazarus) was a 76 year old man who craved immortality.
Lazarus was only a child during the Second World War but had vivid memories of it. He spoke to his associate Lady Thaw of how he feared death, and sat in Southwark Cathedral during the Blitz. He also spoke of how he and others would sit in the crypt; the living amongst the dead.
Lazarus' lust for immortality came from the fact that he wanted to spend another lifetime on Earth so he could continue his work. His anti-aeging device managed to make him seem 30 years younger and was planning to make the device public.
The Doctor and Martha encountered him when they discovered Martha's sister Tish had got a job with him and was on the news.
During the party that took place celebrating the device, the Doctor used a DNA sample from Martha's hand when Lazarus had kissed her to find out about his DNA. The DNA had changed and had unlocked a gene from a once forgotten type of evolution that had died out, but the gene had layed dormant inside the human race until Lazarus had activated it.
The unlocking of this gene transformed Lazarus into a huge skeletal scorpion-like beast that fed on the life of it's victims by absorbing energy with it's whipp-like tail.
The creature was immune to fire and could become human again when it wanted to, but had to transform to feed. The Doctor told it that nature had got it's revenge on him and made him into a joke.
The creature was seemingly defeated when the Doctor rewired the anti-aeging device so instead of harming anything inside the capsule it harmed the outside. Lazarus was not killed and woke up in an ambulance had killed to medics and had a final showdown in Southwark Cathedral. Martha and Tish lured the beast up to the bell tower and the Doctor caused it to drop by playing the pipe organ as high as it goes (with the help of the Sonic Screwdriver that interferes with Lazarus' sonic equipment. Lazarus transforms one last time into elderly form, this time permanently dead.
