Enemy

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)

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)

Bilis Manger claimed to Gwen Cooper that he was not her enemy. (TV: End of Days)

The Uvodni and the Malakh were enemies who were engaged in a war before an armistice was signed. General Uvlavad Kudlak, however, was deceived into collecting human soldiers for the next ten years by the Mistress, an Uvodni computer whose creed was that the Uvodni would "not suffer [their] enemies to live." When this deception was exposed by Luke Smith, Kudlak deemed that his enemy were not the Malakh but the Mistress and, repeating her creed, terminated the computer. (TV: Warriors of Kudlak)

When Sarah Jane Smith disappeared, Clyde Langer suggested making a list of all her enemies. Rani Chandra remarked that that would take fifteen years. (TV: The Temptation of Sarah Jane Smith)

Blamed for the failure of the Bane invasion of Earth and the death of the Bane Mother, Mrs Wormwood was branded an enemy of the Bane Kindred. (TV: Enemy of the Bane)

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

Of the Doctor
The Eleventh Doctor told Winston Churchill that the Daleks were his oldest and deadliest enemy. Infuriated at seeing the Daleks pose as British Army soldiers in the Ironside Project, the Doctor raged to a Dalek that it was his enemy and he was theirs. (TV: Victory of the Daleks)

The Seventh Doctor told Ace that was one of his oldest and deadliest enemies. (TV: Survival) The Eighth Doctor identified the Master as his "old enemy". (TV: Doctor Who)

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 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)

Of the Daleks
Upon being branded an enemy by the Supreme Dalek, 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)

The Seventh Doctor acknowledged that he was the "mortal enemy" of the Daleks while goading one during the Shoreditch Incident. (TV: Remembrance of the Daleks)

As noted by the Tenth Doctor, the Cult of Skaro's job was to "think as the enemy thinks". Having caught his image on a communications barrier with the Cybermen, Dalek Jast recognised this incarnation as an enemy, though it took Rose Tyler to confirm that he was indeed the Doctor. (TV: Doomsday)

The Eleventh Doctor realised too late that the Daleks used the Ironside Project to goad him into identifying himself. He, as their greatest enemy, provided a testimony which caused the progenitor to accept the impure Daleks and create a New Dalek Paradigm. (TV: Victory of the Daleks)