Gold Dalek (Day of the Daleks)

The Gold Dalek was a Supreme Dalek and a member of the Dalek Supreme Council. It specialised in time travel-based operations. (PROSE: Dalek: The Astounding Untold History of the Greatest Enemies of the Universe) The Time Lords believed this Dalek to be a subordinate "outpost commander" who deputised for the Dalek Supreme. (PROSE: Dalek Combat Training Manual)

Alliance with the Master
On the eve of the Second Dalek War of the 26th century, the Gold Dalek led a platoon of Daleks to meet on the Ogron homeworld. There, it ordered the Master's captives — including the Third Doctor, Jo Grant, General John Williams and the Draconian Prince — exterminated. However, the Master convinced the Daleks to leave the prisoners under his supervision until the Daleks' planned war began so he could see the galaxy in ruins, to which the Daleks agreed and left the planet. Later, the Doctor managed to escape the prison cell by using the Master's hypnosound device, which caused the Ogron on guard to perceive the Doctor as the Gold Dalek and he opened the cell out of fear. (TV: Frontier in Space)

Fallout of failure
The Gold Dalek's decision to ally with the Master having led the Daleks to a defeat on Spiridon that set the Empire's war efforts significantly, even causing them the loss of another Dalek Supreme. (TV: Planet of the Daleks) As the Gold Dalek felt responsible for the failure, to redeem itself, it orchestrated a time travel-based mission to conquer Earth in the 22nd century, creating an alternate timeline.

However, this order of events was only outlined by human historians. (PROSE: Dalek: The Astounding Untold History of the Greatest Enemies of the Universe) It was also possible this "Time Paradox Incident" actually occured before the alliance with the Master from the Daleks' perspective, as that was the order the Time Lords recorded the events in. (PROSE: Dalek Combat Training Manual) Indeed, the Gold Dalek did not recongise the Third Doctor during this incident despite his role in defeating their plan with the Master. (TV: Day of the Daleks, Frontier in Space)

Ruler of Earth
The plan allowed it to become the Supreme Dalek in charge of the planet Earth in the ensuing alternate timeline where the Second World Peace Conference had failed and the Daleks invaded in the 22nd century in the aftermath of the devastating wars which followed.

When the Third Doctor threatened to negate the timeline, the Gold Dalek led the Daleks and their Ogron servants back to the 20th century to ensure the Conference failed and their favoured timeline continued. The Gold Dalek had the Doctor interrogated through the use of the Mind Analysis Machine, and saw depictions of the First Doctor and the Second Doctor. They advanced into the Auderly House which was then destroyed by Shura using a Dalekanium bomb, taking them with it. (TV: Day of the Daleks)

Legacy
According to the human historians, 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)

Prop
In Day of the Daleks and Frontier in Space, the Gold Dalek was depicted with a hybrid prop combined from a top half constructed for The Chase and a bottom half constructed for The Daleks.

Identity
Although the same prop was used, it was not confirmed until Dalek: The Astounding Untold History of the Greatest Enemies of the Universe that the Gold Daleks in Frontier in Space and Day of the Daleks were the same individual.