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. It first appeared in print in The Discontinuity Guide.

Summary
In one timeline, Davros created the Daleks, who actually, not just apparently, exterminated him. In this timeline, the Daleks develop full time travel and, except for a brief civil war during the events of The Evil of the Daleks conquer as a united force.

In the second timeline, created by the Doctor's intervention in Genesis of the Daleks, Davros appears to die, but, in truth survives in a dormant state. The Daleks revive him in Destiny of the Daleks. Later, his survival provokes the Imperial-Renegade Dalek Civil War, which weakens the Daleks, who never develop full time travel. The Seventh Doctor destroys Skaro and perhaps all of the Daleks at the end of Remembrance of the Daleks.

Therefore, while Davros existed in both timelines, Dalek stories set prior to Genesis of the Daleks, and those set after, take place in different continuities.

In the Real World, Davros had never appeared on-screen because up until Genesis of the Daleks because Terry Nation had not invented the character. Various accounts had given different accounts of the creation of the Daleks, which conflicted to a greater or lesser degree from one another. The character of Davros achieved such popularity that various production teams brought him back in later stories.

Canonical support or denial
John Peel's "revisionist" War of the Daleks suggested that, in reality, the Daleks had put into motion a hoax which involved pretending to go to war with the Movellans and staging a fake Imperial-Renegade civil war, which would mean Davros had had a much less disruptive influence over the Daleks than shown on screen. Though a Doctor Who fan, John Peel may or may not have known about the theory.

This theory pre-dates the recent television revival of Doctor Who, which shows Daleks more in line with some previous, which has neither confirmed nor denied it. The new series of Doctor Who has not, to date, touched upon the theory directly, though in continuity terms, the Time Lords attempt to alter Dalek history does feature into the backstory of the Last Great Time War.