8. Romana
Romana is still my favourite companion, so forgive me if I admit a bit of bias here. Her departure was absolutely heartbreaking, and made a perfect sort of sense. A time lady from Gallifrey, she was assigned to help the Fourth Doctor find the Key to Time but became fast friends with him and stayed even after the entirety of season 16 was revealed to be a cruel plot by the Black Guardian. Originally played by the sophisticated Mary Tamm, she eventually regenerated into the slightly more mischievous Lalla Ward and ended up having adventures across multiple universes. Romana was, much like Tegan, an integral part of the show by the time of her departure. She was a time lady, and so the equal of the Doctor in a way that was interesting and different. She sometimes did the running and screaming thing, because Classic Doctor Who was far too fond of that, but usually she was brave and smart and completely noble. It's because of these character traits that her departure works so well she doesn't decide to stop travelling with the Doctor just because she wants to go home, in fact just the opposite. She stops travelling with the Doctor to save lives, to free the oppressed Tharils from slavery and forge her own path. She is as unique in her departure as she was in her tenure. Her departure is also foreshadowed, in a way that's also unique considering that the Classic series sometimes decided to drop companions in the middle of the story. It's part of the E-Space trilogy - a block that consisted of one fantastic story, one great story and one story that introduced Adric. At the beginning of the trilogy Romana is reluctantly called home to Gallifrey, and is only saved by the sudden jump of the TARDIS into another universe. Through this it's established that Romana would rather do anything than return to Gallifrey, and so her departure makes narrative sense. Romana counts as one of the strongest companions that the Doctor has ever had, so why wouldn't she want to say goodbye to him on her own terms? And the fact that pretty much everything is on her own terms is what makes Romana's departure one of my favourites. Few companions get to consent to leaving the Doctor, even in the modern series. Romana, however, chooses her own path just as she always has she makes her decision, and forces the universe to deal with it. I can think of few things more in character. Romana is probably the closest to an equal that the Doctor has ever had, and I feel that her departure shows this perfectly. Noble, brave and fitting perfectly into her narrative arc Romana chooses her own path and does it excellently. I cried for about a day after I watched her departure, but I'm pretty sure that they were happy tears. It was sad to see my favourite companion go, but it was probably the best ending that I could've hoped for.