The Master is a renegade Time Lord who is the greatest individual enemy of the Doctor.

Davros is the Daleks' creator.

The Beast was an ancient being that had been trapped for millions of years in a pit at the centre of the planet named in the Scriptures of the Faltino as Krop Tor, orbiting the black hole designated K37 Gem 5 by humans. The centre of the planet, ten miles down, had a powerful energy source which kept it in constant gravitational balance against the pull of the black hole. This counterweight extended out in a funnel into open space.

The Beast claimed that he was the basis of the Devil-figure in all religions and mythologies, and originated from before this universe's creation. He had been defeated and trapped beneath the planet by the "Disciples of Light", who had crafted his prison such that if he ever freed himself, the gravitational force would collapse and the planet would be pulled into the black hole, destroying them both.

The Rani is a renegade Time Lord, an evil scientific genius whose villainy comes not from the usual variety of lust for power and suchlike, but from a mindset that treats everything (including morality) as secondary to her research; she has been known to enslave entire planets such as Miasimia Goria in order to have a ready supply of experimental subjects and a place to carry out her experiments uninterrupted. Her major interest is in tinkering with other species' biochemistry — she was exiled from Gallifrey after some of her lab mice, as a result of an experiment, grew to enormous size and ate the President's pet cat.

She can regenerate, and if her mice could grow enormous, it's likely that she is now big!

Ood are creatures possesed by the beast

monstrous slug-like extraterrestrial who could control minds.

The Abzorbaloff is a monster designed by nine-year-old William Grantham of Colchester, Essex for a "Design a Doctor Who Monster" competition.

The Family of Blood are a family who appear in the Series 3 episodes "Human Nature" and "The Family of Blood" (2007) in which they are the titular entity. They are incorporeal, green telepathic creatures and refer to each other as "Father of Mine" (or "Husband of Mine" in Mother's case), "Mother of Mine", "Son of Mine" (who appears to assume leadership, and thus the naming of the others is compared to him) and "Sister of Mine". Because of their lack of form, they required a physical body to inhabit; they only had short lifespans without them and as such, sought that of a Time Lord. They had a time vortex manipulator allowing them to time travel. Their spaceship was stolen and was protected by an invisible shield. They could also animate different things for servants — in the case of their 1913 invasion of Earth, scarecrows — using "molecular fringe animation". They also possess hand-held energy firearms capable of disintegrating flesh and cloth.

Lady Cassandra is the last human who cause much trouble for the Doctor including possessing his body.

Blon Fel-Fotch Pasameer-Day Slitheen portrayed by Annette Badland and Alan Ruscoe, was a member of the nefarious Slitheen crime family. She appropriated the identity and appearance of Margaret Blaine, an MI5 official who was killed by the Slitheen so that her skin could be used as a disguise. The Ninth Doctor met her in Downing Street in "Aliens of London" when she and her family tried to push the Earth into a nuclear war, and use the remains of the planet for fuel. She was apparently killed when the Doctor helped Mickey Smith blow up No. 10 with a missile. It was later revealed in "Boom Town" that while the rest of her family had been killed, she had teleported out at the last minute. She had then gone on to become the lord mayor of Cardiff in the six months between the stories, and was planning to use the Cardiff Rift in conjunction with a planned nuclear power station to destroy the planet and use a tribophysical waveform macro-kinetic extrapolator to ride the shockwave into space, to find any surviving members of her family. The Doctor stopped this, and was going to send her back to her home planet, even though she would be executed. She tried to use the extrapolator in conjunction with the Rift and the TARDIS to execute her plan without the Power Station, however the TARDIS console broke open and she was exposed to the "heart of the TARDIS" the time vortex and with the Doctor's encouragement was regressed to an egg. The Doctor, Rose Tyler, and Jack Harkness then took her to the nurseries of Raxacoricofallapatorius so that she could start her life afresh.