Theory:Timeline - Daleks

The Dalek timeline theory speculates that the Daleks have two timelines. The first, Davros really did die when exterminated by the Daleks after their creation.

In another, Davros only appeared to die, but lived, and his survival provoked the Imperial-Renegade Dalek Civil War, which weakened the Dalek species. The Fourth Doctor created the second timeline, inadvertantly, when the Time Lords sent him to Skaro in Genesis of the Daleks. Therefore, Dalek stories set prior to Genesis of the Daleks, and those set after, take place in different continuities.

In the Real World, Davros never appeared on-screen because up until Genesis of the Daleks, Terry Nation had not invented the character.

The theory originated in the The Discontinuity Guide.