Davros's accident

As the Sixth Doctor understood, Davros was crippled as the result of what he called an "accident". (AUDIO: The Juggernauts)

The event occurred one month after the death of Calcula, Davros's mother. Davros was in fact grievously wounded by a Thal bombardment of his laboratory in the Kaled Dome which cost him his taste buds, left arm and entire lower body and left his eyes with severe damage to the point where using them would cause great pain. (AUDIO: Davros, Corruption) Although the reinforced walls of the lab prevented the bombardment from killing the Kaled scientist, (AUDIO: From the Flames) he was forced to spend the rest of his life confined to a mobile life support system attached to a wheelchair, with an eyestalk-bulb in his forehead that gave him partial eyesight without the use of his own eyes.

After he was crippled, the Scientific Corps gave Davros a projectile poison injector to allow him to kill himself. He kept it but refused to use it. (AUDIO: Davros, Corruption) In his life-support system, Davros was identified as a mutant. (TV: Destiny of the Daleks) According to some accounts, he based the design of the Dalek casing off his life-support chair. (PROSE: The Whoniverse, et. al) However, the idea of what would one day be realised as the Dalek casing were already starting to form in Davros's imagination by the time of his accident. (AUDIO: From the Flames)