Enemy

According to the Twelfth Doctor, an enemy was "just a friend you don't really know yet." (WC: Prologue) According to the Eleventh Doctor, "everyone [had] enemies." (TV: Victory of the Daleks) Ohila claimed that anyone could hide from an enemy, but no one could hide from a friend. (WC: Prologue) In regards to his relationship with the Daleks, the Seventh Doctor told Ace that one could "always judge a man by the quality of his enemies." (TV: Remembrance of the Daleks)

After failing to deceive the Twelfth Doctor into destroying a Daleks casing containing Clara Oswald, claimed that she "gave" Clara to him to make him see "friend inside the enemy" and "enemy inside the friend". (TV: The Witch's Familiar)

Sutekh identified all life as his enemy. (TV: Pyramids of Mars)

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)

During World War II, Winston Churchill voiced his belief that the Ironside Project would bring death to the enemies of Britain, the Third Reich.

Amy Pond identified a woman outside Budgenss with a mental Jack Russell as her enemy. (TV: Victory of the Daleks)

Of the Doctor
The Third Doctor identified to Sarah Jane Smith as his "best enemy", (TV: The Five Doctors) which was repeated by  as he revealed himself to the Thirteenth Doctor and Team TARDIS. (TV: Spyfall) The Fourth Doctor noted to be his "sworn archenemy". (TV: The Deadly Assassin) 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) Fatally shooting the Eleven, claimed that "the Doctor already has a greatest enemy, he doesn't need another." (AUDIO: Day of the Master)

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. It was through this encounter that Amy Pond realised that the Doctor had not only enemies but archenemies. (TV: Victory of the Daleks)

The Ninth Doctor identified the head of a Cyberman in Henry van Statten's vault to Rose Tyler as an "old friend of mine. Well, enemy." (TV: Dalek)

The Twelfth Doctor claimed Davros to be his archenemy much to the jealousy of, the female incarnation of the Master. (TV: The Magician's Apprentice) Indeed, Ohila noted that the Doctor and Davros were enemies for all the "long time" they had known each other. (WC: Prologue)

Within a Big Brother House aboard the Game Station, the Doctor told Lynda Moss that he had to know his enemy to get out. (TV: Bad Wolf)

As he noted in a holographic projection, Emergency Program One was to be used in the face of an enemy that could not be allowed to obtain the Doctor's TARDIS. (TV: The Parting of the Ways)

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)

During the Siege of Trenzalore, Mother Superious Tasha Lem saw that the Papal Mainframe strove to maintain the peace between the Eleventh Doctor and his enemies. Claiming that "all the Time Lord's enemies" came to the fields of Trenzalore, Tasha recalled the sight of the Doctor standing back to back with his ancient enemies, the Silence, until only the Daleks remained in their path. (TV: The Time of the Doctor)

Of the Time Lords
The The Record of Rassilon identified the King Vampire as an enemy of the Time Lords, giving instructions to kill him even at the cost of one's own life. Likewise, the Three Who Rule knew the Time Lords as enemies of the King Vampire, who they worshipped as the "Great One". (TV: State of Decay)

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) A most prolific subject of their hatred was the Time Lord known as the Doctor, who most Daleks sought to kill on sight. (TV: Remembrance of the Daleks, Dalek, Evolution of the Daleks)

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)

Daleks operating a Dalek time machine identified the First Doctor and his three "human" companions, Ian Chesterton, Barbara Wright and Susan Foreman, as their "greatest enemies" who were responsible for "delaying" their conquest of Earth. Pursuing the Doctor's TARDIS, they knew it as the "enemy time machine" or simply "enemy machine". (TV: The Chase)

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) The Tenth Doctor noted himself to be the Daleks' "number one enemy". (TV: Evolution of the Daleks)

The Dalek named Metaltron by Henry van Statten, upon hearing the Ninth Doctor identify himself, branded him the enemy of the Daleks and intended to kill him only to find that its gunstick did not work. (TV: Dalek)

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)

When the Cult of Skaro were confronted by the Doctor in New York in 1930, Dalek Caan noted him as "the enemy of the Daleks." In Hooverville, Dalek Caan intended to be "the destroyer of [the Dalek's] greatest enemy" but was stopped by Dalek Sec, now a Human-Dalek. Sec had come to believe that Davros was wrong to remove the emotions of the Daleks, that it made them not stronger but lesser than their enemies. However, Sec was soon overthrown by his fellow Daleks, who deemed him to be an enemy of the Daleks in addition to the Doctor. As Dalek Jast opened fire on the Daleks' greatest enemy, Sec took the shot and died instantly. It was the loss in this encounter with his "age old enemies" that motivated the Doctor to save Lazlo's life. (TV: Evolution of the Daleks)

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)

While within a Dalek casing, Clara Oswald's statement to the Twelfth Doctor, "I am your friend.", became "I am your enemy." (TV: The Witch's Familiar)

Of the Cybermen
A Cyberman from Telos knew the Doctor as an enemy of the Cyber race. (TV: Attack of the Cybermen)

Manipulating a group of Cybermen that had been Time Scooped to the Death Zone, told them that the Time Lords were their enemies. (TV: The Five Doctors) In 1851, the Tenth Doctor identified himself to Jackson Lake as "enemy of the Cybermen." (TV: The Next Doctor)

Of the Sontarans
The Sixth Doctor noted that the Sontarans and the Rutans were "old enemies" who fought in a war that lasted so long they had forgotten what started it. (TV: The Two Doctors) The Doctor was also known as an enemy of the Sontarans and a facechanger. (TV: The Sontaran Stratagem)

Behind the scenes

 * The Ninth Doctor deemed his upcoming marriage to Emma to be news even his archenemy, the Master, needed to hear. When the Master vowed that he would renounce evil following the apparent death of the Twelfth Doctor, the Daleks, noting that he saved them from the zectronic beam, decided to likewise honour their mortal enemy. (NOTVALID: The Curse of Fatal Death)