Enemy

You may be looking for the enemy of the Time Lords during the War in Heaven or humanity's enemy formed by the Committee.

According to the Twelfth Doctor, an enemy was "just a friend you don't really know yet." (WC: Prologue)

At the end of the Thousand Year War, Gerrill of the Mutos believed all non-mutated Kaleds and Thals, known as norms, to be enemies who deserved death for their treatment of his kind. (TV: Genesis of the Daleks)

The Eighth Doctor identified the Master as his "old enemy". (TV: Doctor Who)

Approaching the Nestene Consciousness during the 2005 Nestene invasion of Earth, the Ninth Doctor failed to convince it that he was not its enemy. (TV: Rose)

The Tenth Doctor was identified by the Torchwood Charter of 1879 as an enemy of the British Crown. Torchwood One director Yvonne Hartman used that to explain how he was not aware of Torchwood until being led to Torchwood Tower in 2007. As he was the enemy, the Doctor correctly realised that he had become Torchwood's prisoner. (TV: Army of Ghosts)

In 1851, the Doctor identified himself to Jackson Lake as "enemy of the Cybermen. (TV: The Next Doctor)

Acknowledging that Wilfred Mott had seen his enemies, the Doctor claimed him that the Time Lords coming from the last day of the Last Great Time War were more dangerous than any of them. Later, the Doctor stood between the Saxon Master and Rassilon with a gun pointed at the former. The Lord President warned the Doctor in vain to choose his enemy well, noting that the Time Lords were many while the Master was one. (TV: The End of Time)

Daleks

Upon being branded an enemy by the Supreme Dalek, Missy claimed that anyone who was not a Dalek was an enemy of the Daleks. (TV: The Witch's Familiar)

Indeed, one of the first Daleks created by Davros decreed that all "inferior creatures" were to be considered the enemy of the Daleks and destroyed, proceeding to exterminate the Kaled Scientific Elite and seemingly Davros himself. (TV: Genesis of the Daleks)

Having caught his image on a communications barrier with the Cybermen, the Cult of Skaro recognised the Tenth Doctor as an enemy, though it took Rose Tyler to confirm that he was indeed the Doctor. (TV: Doomsday)