Black Dalek (The Curse of Fatal Death)

A Black Dalek with golden adornments was in charge of the Dalek squadron who joined the Master during his face-off against a series of regenerations of the Doctor (starting from the Doctor's ninth body).

Though it did not formulate the deal, the Black Dalek honored one of its underlings' promise to the Doctor to spare him if he helped save them from the zectronic beam going haywire and wiping the Daleks out. As the Twelfth Doctor lay dying, the Black Dalek first reinstated that he would not be harmed by the Daleks if he survived. When it became clear that the Doctor was indeed dead, the Black Dalek then vowed, in the name of the entire Dalek race, to honor their former foe who had died saving them. After the Doctor, against all known laws of the universe, regenerated into a thirteenth self, the Black Dalek and its forces indeed let this new Doctor depart alongside the Master — nor did they make any move against the Doctor's companion Emma. (TV: The Curse of Fatal Death)