Time Paradox Incident

The Time Paradox Incident was the Time Lord designation for the event in which the Third Doctor prevented the assassination of Sir Reginald Styles. (TV: Day of the Daleks, PROSE: Dalek Combat Training Manual)

Led by the Gold Dalek, the Daleks used time travel to invade and occupy Earth again, their previous attempts having met with failure, exploiting the outbreak of World War III on Earth in the 20th century. Guerilla fighters opposing the Daleks' occupation in the 22nd century used time travel of their own to attempt to avert the war that had given the Daleks their opportunity, unaware their actions would actually precipitate the conflict and paradoxically enable the very invasion they were fighting. Their visits to the past embroiled UNIT and the Third Doctor currently serving as their scientific adviser. (TV: Day of the Daleks)

Legacy
Informed by the failure of the Gold Dalek, one of the remaining Dalek Supremes later organised a smaller-scale time mission, (PROSE: Dalek: The Astounding Untold History of the Greatest Enemies of the Universe) going further back along the timeline of the Doctor and attempting to execute him in his first incarnation. (TV: The Chase)

Though the alternate timeline in which the Daleks conquered Earth was averted by the Doctor, The Dalek Conquests suggested that the incident had brought the Daleks to the attention to the Time Lords, who would later assist the Third Doctor in the Spiridon campaign. It was further suggested that the incident motivated the Time Lords to plan their "future strategy", leading to the Last Great Time War. (AUDIO: The Dalek Conquests) It was during the Time War that the Daleks, through the Overseer, rewrote history so that they used Ogron mercenaries during a number of skirmishes with the Doctor, but did not rewrite it enough so that their outcomes changed. As a result, the Eighth Doctor recalled the Ogrons' presence in these pre-war incidents. (AUDIO: Planet of the Ogrons)

Alternate universes
In the Unbound Universe, where the exiled Doctor arrived on Earth in 1997, the Brigadier had seen three Daleks kill 47 of his men in 1972, which was later cited as evidence of his incompetence. Since then, the Daleks had visited Earth "several times". He recalled the initial encounter when he saw the Daleks on Skaro. (AUDIO: Masters of War)

Behind the scenes

 * Episode four of Day of the Daleks was originally intended to include a confrontation between the Doctor and the Daleks, in which the Daleks explained how they destroyed those of their number who were infused with the Human factor in The Evil of the Daleks, and turned their attention to conquering Earth by means of time travel. But this scene had to be edited out, due to the episode overrunning. Bringer of Darkness would later establish the Doctor having been made aware earlier, whilst still in his second incarnation, that the Daleks had survived "the Final End".