Luke Rattigan
Luke Rattigan was a gifted and ambitious teenager who developed the Atmos car technology in cooperation with the invading Sontaran species. He was the founder of the Rattigan Academy.
Biography
At 12 years old, Luke invented the "Fountain 6" search engine, which made him into a millionaire almost overnight. In his later teens, feeling misanthropic and underappreciated by society, he cooperated with the Sontarans to develop the "Atmos" car device, which effectively eliminated all CO2 emissions of a car but would also poison the Earth atmosphere so the Sontarans could build a clone army to fight their own war against the Rutan Host.
The Doctor arrived when the then-18-year-old Rattigan was directing his own Rattigan Academy, which was made up of other similarly gifted teenagers, handpicked by Rattigan. Unbeknownst to any of them but Luke, the Sontarans had promised to give them nonexistent "Castor 36" planet (renamed "Earth-Point-Two" by Rattigan) on which they could build a new world after the poisoning of Earth.
Eventually, the Sontarans activated their "Atmos" devices, which had already been installed into the 50% of the world's automobiles. The Atmos systems emitted a gas which would incapacitate all humans for their cloning process and such cloud was soon wrapping the whole planet. Overcome by the thrill of war, Luke teleported from the Sontaran ship where he'd been watching the gas cloud eneveloping the planet back to his academy, and tried to convince his pupils of his academy to come with him to "Castor 36" to found their own civilization (for which they had been developing superadvanced technology in their labs). However, horrified by the disaster and assuming Rattigan to be mad, they abandoned him and fled.
A dejected Luke returned to the Sontaran mothership and reported his failure. The Sontarans revealed they had had no plans to keep the students alive anyway, and had merely needed Luke and his pupil for the creation and installation of the Atmos systems. Devastated, Luke teleported again back to Earth and he was met again by the Doctor, who told him to "do something clever with his life". The Doctor teleported to the Sontaran ship with a reversed Atmospheric Converter, with the intention to blow up the Sontarans—and himself in the process—if they refused to leave Earth alone. Taking the Doctor's advice, Luke reprogrammed the teleporter, switched places with the Doctor, and blew up the alien ship just in time, killing himself in the process. When Martha and Donna (who were present on earth with the Doctor) asked him what he was doing when he reprogrammed the teleporter, he said, "Something clever." (DW: The Sontaran Stratagem/The Poison Sky)
When Davros asked the doctor "How many have died in your name?", Rattigan appeared in a flashback of people that have died. (DW: Journey's End)
Personality
Even though Luke was incredibly brilliant, he had several mental problems. Many times he behaved almost neurotically, in an outburst of unreasonable emotion. It seemed that the reason for Luke's problems was because of lack of social skills, which was shown when he believed all his students had been rejected from society for being intelligent. He was very ambitious, and callous towards people he felt were not up to his standard of intelligence. He found the Doctor particularly annoying because of his cheeky attitude combined with his obvious intelligence. Luke appeared to have joined forces with the Sontarans because they appreciated his genius, leading him to commit global treason. In the end the Sontarans turned against him and Luke redeemed himself by sacrificing his life to destroy them. (DW: The Sontaran Stratagem/The Poison Sky)
