Davros Singing his heart out.
Davros was a Kaled who created the Daleks by genetically modifying his own race. The products of his research eventually killed all the Kaleds, including him, and became the Daleks.
He was resurrected one hundred thousand years later, however, and began work on a grand scheme which involved creating a new race of Daleks that would obey only him. He experimented with bonding flesh and machine to create the perfect Dalek. This was seen as disgusting by the original Daleks who hunted him down. He pretended to be a head in a jar, calling himself the 'Great Healer', ironic since he created the Daleks, the greatest killing machines ever. When the Daleks finally did capture him he was half mad, partly because of his twisted fate and partly because being in a jar all day really takes its toll on you.
Davros in his younger years
Davros was held by the Daleks for many years but took his chance to escape around the time of the Dalek Civil War. He managed to become Emperor of the Imperial faction of Daleks, with the Original Daleks being dubbed the 'Renegade' Daleks. Davros incorporated his idea of cyborg Daleks into his Imperial minions, which made them obey him even after he revealed himself. This gave the Renegades even more reason to fight the war.
The conclusion to the war remains unclear, and no-one really knows which side won. However, what is clear is that Davros lived to see the start of the Time War, after an embarrasing defeat at the hands of the Doctor via the Hand of Omega, but he was pulled out of the war by Dalek Caan, who went insane trying to rescue the creator of the Daleks.
Davros in his chair
Davros set to work rebuilding the Dalek race using cells from his own body, leaving him even more crippled. The Daleks he created once again betrayed and imprisoned him, but at this point he had grown to not care. He continued his research and eventually created a thing called a Reality Bomb. He wanted to destroy all of reality, leaving the Daleks the only things in the universe. Even the Daleks knew this was a rubbishy plan, but they couldn't think of anything else to do so they agreed. Not only that, but Dalek Caan, despite beign insane, was being heralded as a prophet and foretold the destruction of all things and the victory of the Daleks.
However, the Doctor and his companions found Davros and the Daleks and fought them to a standstill, and after the Supreme Dalek was anticlimactic blown up by Captain Jack Harkness, the Doctor's trusted second, Davros eventualyl realised the Truth: Dalek Caan had lied to them.
When Davros asked him why, Caan said he had seen all of time and space and all the horrors that the Daleks had ever committed, and he had condemned them. In the blazing fire that was his flagship, Davros raged at the ruination of his plans, and Dalek Caan laughed maniaclly as the Dalek race burnt.
