Luke Rattigan
Yeah, well, see, that's a tautology. You can't say Atmos system because it stands for "Atmospheric Omission System". So you're saying Atmospheric Omission System System. Do you see Mr Conditional Clause?
Luke Rattigan was a gifted teenager who developed the Atmos car technology in cooperation with the invading Sontaran species. Also, Rattigan was the founder of the Rattigan Academy.
Life
Being just 12 year old, Luke Rattigan invented the "Fountain 6" search engine, becoming a millionaire overnight by this reason. Then, feeling misanthropic and underappreciated by society, he cooperated with the Sontarans to develop the "Atmos" car device, which effectively eliminated all CO2 emissions of car but which would poison the Earth atmosphere in time for the Sontarans' stratagem. Then, the aliens would 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 formed by other gifted teenagers of similar profile. For all them, the Sontaran had promised the nonexistent "Castor 36" planet, which would be renamed "Earth-Point-Two" by Rattigan.
Eventually, the Sontarans activated their "Atmos" devices, which had already been installed into the 50% of all world automobiles. They emitted a gas which would incapacitate all humans for their cloning process and such cloud was soon wrapping the whole planet. Declaring war, Luke got a magnificent demeanor and tried to convince his pupils of his academy to come with him to "Castor 6" and to found their own civilization (for which they had been developing things in their labs). However, they abandoned Rattigan then, thinking he was mad.
Luke returned to the Sontaran mothership and told the Sontarans of his failure. The Sontarans revealed they had no plans to keep them alive anyway and merely had needed Luke and his pupils, at that point, "for installation of the Atmos system." 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 again to the Sontaran ship to suicide bomb the Sontarans but Luke used the teleportation device timely to make him come back and in return Luke took his place on the ship and used his invention, the Atmospheric Converter to blow up the Sontaran ship, killing himself and the Sontarans. This action saved the Earth.
When Davros reminded the doctor "Every Where You go there are always deaths" Rattigan appeared in a flashback of people that have died. (DW: Journey's End)
Personality
It's been a long time since anyone has said no to you, isn't it?
Even though Luke is incredibly brilliant, he has several mental problems.
Luke finds the Doctor annoying because of cheeky attiude and intelligents.
It seems that the reason for Luke's problems is because of his the lack of social skills, which is shown when he believes all his students have been rejected from society for being smart.
Luke finds murder and suffrage of humans entertaining because of his hatred towards the world, but cannot find the strength to murder himself.
Luke appears to have joined forces with the Sontarans because they appreciated his genius leading him to commite global treason, but after he was betrayed by the sontarans, he was left alone and broken.
With the result of him comitting self sacrifice to save the world, his personal view of the world is unknown, whether he did this to save the world and do something with his life or just as revenge against the the sontarans who betrayed him is unknown.
