Richard Lazarus is the secondary antagonist in the third season of the Doctor Who revival series.
He was an elderly scientist and a close ally of Harold Saxon who feared death and wished to avoid it and restore his youth. He finally managed to achieve this goal after striking a deal with Saxon on funding the technology. Although it restored his youth the technology drastically mutated his DNA beyond repair.
He was portrayed by Mark Gatiss, who also serves as one of the series' writers.
Lazarus was born shortly before the Second World War and grew up in the middle of the chaos it caused. On one night of the Blitz he hid himself inside of the Sothwark Cathedral, traumatised at all of death and mayhem surrounding him. Although he lived Lazarus was extremely psychologically damaged, swearing to himself he would never face death again.
Growing up Lazarus gained wealth and recognition as a genius scientist and married sometime in his adulthood.
Deal with Saxon
During his rise to power The Master/Harold Saxon approached Lazarus and the two struck a deal to get what they both wanted. The Master agreed to fund Lazarus' technology and the experiment to restore his youth on the conditions that he get his own supply of the tech built into his laser screwdriver and that Lazarus ensured to hire Tish Jones as the head of his PR department in an attempt to lure The Doctor and Martha Jones into his grand plan.
Eventually Lazarus managed to build the machine to reverse the ageing progress and shows it off in a public.
During the demonstration Lazarus steps inside the machine to test it out, however it goes haywire and The Doctor moves in to shut it down and avoid the building and Lazarus himself getting destroyed. Lazarus then stepped out of the machine looking roughly four decades younger and the crowd are astonished with the machine deemed a success. While celebrating however Lazarus quickly began experiencing rapid muscle spasms, bone crunches and extreme hunger for unknown reasons. The Doctor and Martha while investigating discovered that the machine activated dormant genes in his DNA, unfortunately however they were too late to move in to stop the inevitable and Lazarus uncontrollably begins to transform into a evolutionary throwback which can suck up the life energy of humans at random periods of time.
The beast chases the party guests throughout the building and ultimately The Doctor and Martha who decided to hide in his machine. Lazarus then turned the machine on however in an attempt to mutate the duo, however the Doctor reverses the polarity which causes it to blast Lazarus, injuring him greatly. When he he taken away by an ambulance, he woke up and killed the medics inside and escaped to Sothwark Cathedral once again closely followed by the Doctor.
He then told The Doctor of his childhood and motives for avoiding death to which The Doctor attempts to talk reason into him from, his pleas fall on death ears however as Lazarus claims that he's progressed so far and won't give it up, inevitably he transformed back into the monster and chased Martha and Tish up to the bell tower. The Doctor then makes his way to the pipe organ, amplifies the sound of it to defeaning levels and plays it. The noise made Lazarus lose control of his balance causing him fall from the tower where he died from impact.
After Lazarus died The Master placed Tish into a position of authority at his office and began getting his agents to tap into the Jones family through their phones, laptops, etc in order to track down The Doctor and Martha. Eventually he succeeded in this, apprehended the entire Jones family with the exception of Martha and her brother Leo and imprisoned both Captain Jack Harkness and The Doctor. Before doing this however The Master used his laser screwdriver to torture The Doctor by using Lazarus' built in tech to age him drastically.