It's lonely business, being basically immortal and traveling time and space in a body that never ages. Which is why the last remaining Timelord always brings along a friend! Usually a woman, usually from Earth, always somebody kind of amazing. Here, we rank them from mildly interesting to all-out timey-wimey.
We're sticking to the current series (Ninth, Tenth, Eleventh and Twelfth Doctors). Also considered are companions who joined for just one episode of a special.
Rosita (Velile Tshabalala) is technically the companion of Jackson Lake, who thought he was the Doctor thanks to Cyberman shenanigans. Once she knocked villain Miss Haritgan square in the jaw, we knew Rosita was a tough Victorian who packed a punch.
Captain Adelaide Brooke (Lindsay Duncan) takes drastic measures not only to maintain the continuity of time and space, but also save the Doctor from himself. Principled and good hearted, her one-off time as companion reminds the Doctor (and us) why he always needs a friend in his corner of time and space.
The aristocratic burglar (Michelle Ryan) uses her very particular set of skills to save the Doctor, herself, and others from a pesky wormhole alien encounter. She would've made a cool long-term companion, if the Doctor hadn't been so hung up on his past ones (but mostly Rose).
Pop star Kylie Minogue plays the ill-fated Astrid Peth whose short and bittersweet foray as the Doctor's companion has us wishing she was able to travel time and space with the Doctor for a longer time.
Dear Donna Noble is most likely the funniest of all recent Doctor Who companions. But as a time-traveling partner, she's no joke.
She saves all of her creation and doesn't even remember it! We'll always remember her, though, as the Doctor's "best mate" who didn't need a romance arc with him to keep their relationship fresh.
Martha Jones (Freema Agyeman) has a rocky start as companion to a Rose-mourning Doctor. But she soon proves herself as one of the Doctor's most brilliant counterparts.
After doing a little thing like, oh, you know, preventing the end of the world, the med student evolves into paranormal warrior and a doctor in her own right. (Just not that kind of Doctor.)
Amy Pond (Karen Gillan) started off with a super annoying selfish streak, and yet, she grew to become one of the Doctor's bravest companions.
With Rory and the Doctor in tow, Amy Pond is capable of anything ... including giving birth to a woman who herself becomes one memorable time-traveler.
She was never a romantic interest, but that's what really made her interesting. That and the fact that there was, literally, more than one Clara.
Known as Clara Oswald, Oswin Oswald or Clara Oswin Oswald, she's the Impossible Girl because she's impossible to keep track of. Some iterations have more depth than others; we can't help but pour one out for poor Oswin Oswald, who ... never mind. It's too painful to think of.
Meanwhile, the current Clara is getting more complicated and strong the more she travels with Peter Capaldi's Twelfth Doctor.
Of all of the companions, no one served up more intrigue (or sheer worry on the Doctor's behalf) more than River Song.
Her complex, albeit undeniable, chemistry with the Doctor (she is his wife, after all) establishes her as one of the most dynamic Doctor Who characters, let alone companions. Then again, at one point, she's also destined to be the Doctor's killer.
One of the Doctor's most enduring companions, Sarah Jane Smith (Elisabeth Sladen) also has set off on adventures during the tenures of the Third, Fourth and Fifth Doctors in classic Doctor Who. Her unflappable spirit never wavers when aiding the Doctor, no matter his regenerated form.
The first companion of the revival series, Rose Tyler (Billie Piper) is thoroughly modern and the Doctor's equal.
The relationship she has with the Doctor (or, technically speaking, one version of the Doctor) has to go down as one of the most romantic in the history of science fiction TV.