Richard Lazarus

Professor Richard Lazarus was a man who craved immortality.

Childhood
Lazarus was only a child during World War II but had vivid memories of it. He feared death, and sat in Southwark Cathedral during the London Blitz. Along with others, he would sit in the crypt, the living amongst the dead. His childhood home was destroyed in the bombing.

Genetic manipulation
Lazarus built a Genetic Manipulation Device with financial backing from Harold Saxon. It took him many years to complete, and he was 76 years old when he finished it. When interviewed on Television, he spoke of how his experiment would "change what it means to be human."

The head of PR, Tish Jones, organised an unveiling of the experiment. He stepped into the machine when it was activated. Despite engineering faults, the machine worked, taking thirty years off his age. He stepped out a younger man.

After effects
However, unbeknownst to Richard, the process had activated dormant genes in his DNA. They refused to settle down and so he transformed into an alternate evolution of humanity which fed on human life energy. In this form he killed his associate, Sylvia Thaw, draining her of life energy. Lazarus then returned to human form. He still needed more for the mutation to stabilise and so he took Tish up to the roof, intending to drain her. The Tenth Doctor and Martha Jones interrupted them and ran from him as he again mutated. He chased them down to the main room where he drained another victim.

The Doctor distracted him, leading him to a lab where he caused an explosion. This only angered Lazarus who continued his pursuit. Martha and the Doctor hid within the Genetic Manipulation Device, knowing Lazarus would not want to damage it. Lazarus activated it but the Doctor altered it so that it let out a blast that incapacitated Lazarus. He changed back to human form and, seemingly dead, was taken away by an ambulance.

Death
Lazarus had, however, survived the blast. He recovered and drained the two ambulance men inside with him. He then escaped the ambulance and hid in Southwark Cathedral. He chased Tish and Martha up to the bell tower, mutating again. While he was there, the Doctor used the amplified noise of the Organ to confuse Lazarus, mere seconds before Lazarus could drain Martha. He fell from the tower to his death and his corpse changed once more into his young human form, then into his old form. (DW: The Lazarus Experiment)

Behind the scenes

 * Mark Gatiss, a longtime Doctor Who fan with several writing credits connected with the series, played Lazarus in both his young and old human forms.
 * Neill Gorton claimed that the prosthetic face for the older Lazarus was partially modeled on Vincent Price. (CON: "Monsters Inc.")