Davros was the chief Kaled scientists during the Kaled - Thal war on Skaro. After the Kaleds fired nuclear weapons Davros began experimenting with Kaled mutations. The aim was to find the final Kaled form and to find a way for the Kaled to survive.
Davros created travel machines for the Kaled mutations, and the mark III travel machine, with a Kaled controller, became known as the Dalek.
The fourth Doctor and Sarah first met Davros during a Time Lord mission in which the Doctor was tasked with altering the Dalek's evolution or destroying them. Davros has told the Kaleds that life on other planets was impossible, but after meeting the Doctor learnt that there were many other planets, and learned of Daleks' exploits on other worlds.
Davros programmed the Daleks to have no emotions, and to think of all other species as inferior. This meant the Daleks found Davros inferior and tried to kill him. After reasling they needed an emotional being to defeat robotic Movellans the Daleks returned to Skaro to rescue Davros. After the Daleks' plans were thwarted by the Doctor Davros was arrested by humans, only to be rescued again by the Daleks. After creating a new race of Daleks Davros tried to gain mastery of time thorugh the Hand of Omega.
When the Time War started the Doctor watched Davros die during the first year. Davros was rescued from death by Dalek Caan and taken out of the time lock to create more Daleks and attempt to destroy all of reality.