If the second Doctor has the metonymical soubriquet the Cosmic Hobo, then his predecessor should really be known as the Cosmic Kidnapper – because when you look at it, hardly any of the people who travel with him actually do so of their own accord.
The first Doctor has a bad enough reputation in some circles already (mainly due to that incident with the caveman and the rock very early on) so we should be absolutely clear about this: there is very seldom malice aforethought, it’s just that he’s terribly unlucky about characters wandering into the TARDIS just as he’s about to take off, who end up going along with him as a result.
Of course, his abduction of Ian Chesterton and Barbara Wright at the end of the very first episode is completely premeditated, as is his decision to remove Vicki from the planet Dido (and what hardly appears to have been an especially gruelling lifestyle) very shortly before a rescue mission arrives to collect her. But, to be fair, Steven wanders into the TARDIS interior while delirious, and Dodo, Ben, and Polly all make ill-timed entrances while under the impression that the exterior shell is a genuine police box. (The situation with the two minor companions Sara and Katarina is a little more complex, but neither comes along wholly of their free will.)
If none of these people is with the Doctor by choice, why don’t they just leave straight away? The answer lies in two key differences between the original format and the modern show: the near-total absence from the first Doctor’s era of stories with a contemporary setting, and (the cause of this) the Doctor’s essential inability to control the TARDIS.
People don’t usually travel with the Doctor for fun early on, nor do they find it a particularly pleasant experience. The first couple of seasons in particular are dominated by characters desperately trying to get home. As a result, it’s not that difficult to write characters out convincingly, and most of the departures are voluntary – interestingly, most of the common routines are minted at this point. Susan and Vicki find Love at First Episodes, Ian and Barbara get Home at Last!, Steven Has A Better Offer, and so on. (Sara and Katarina both get Grim Reapered in the same story.)
Things continue in a roughly similar vein in the second Doctor’s tenure – people still aren’t going off with the Doctor because it’s such a fulfilling lifestyle choice, but usually because the alternative is probably a nasty death. Zoe is the first companion on screen who actively chooses to go with the Doctor and leave a (reasonably) pleasant life behind. The early second Doctor departures are similar to those of the first – Home at Lasts! for Ben and Polly, and a sort of Better Offer for Victoria.

Despite their expressions, they really are doing this for fun.
With Jamie and Zoe it gets a little more interesting – Jamie may not have made an informed choice about joining the Doctor, but he’s amongst the most dedicated and loyal followers the Time Lord’s ever had, while, as mentioned above, Zoe is there out of choice. The fact that, really for the first time, this is a TARDIS crew travelling for the fun of it is not much mentioned or considered, but it is a significant innovation. Getting rid of them requires an involuntary departure, and so we end up with the series’ first use of the mind-wipe, administered on this occasion by the Time Lords on their debut appearance.
The series has a whole new dynamic with the third Doctor’s arrival: he doesn’t do a great deal of travelling himself, and his ‘companions’ are really just colleagues from work. The usual ‘Doctor plus boy and girl’ dynamic is initially retained, although they become a man and a woman and the Brigadier is a considerably more complex character, in terms of his narrative role, than a strong-arm foil like Jamie or Ben was. This set-up delivers one of the worst companion departures (Liz Shaw disappears between stories) but also one of the very best: Jo’s final story has clearly been very carefully written in order to make it seem plausible and positive, but at the same time moving. I would personally say that most of the departures from the recent series don’t match up to this one in terms of subtlety and adherence to the series’ traditional style.
From this point on the programme usually sticks to the ‘Doctor plus girl’ dynamic (with occasional quirks such as robot dogs or naval surgeons thrown into the mix), but a more important change has occurred: the TARDIS is now steerable. Not always, but often enough for the Doctor to be able to take a companion back home without it being a noteworthy occurrence (it happens off-screen between The Monster of Peladon and Planet of the Spiders, for instance).
This in turn impacts on the whole dynamic of the series – life with the Doctor can’t be all that bad, or the companion would demand to be taken home. From this point, broadly speaking, they are there by choice. The first person this fully applies to is the peerless Sarah Jane Smith, and the programme acknowledges this by making her departure an involuntary one: she is exiled from the TARDIS when the Doctor has to return to Gallifrey. (The question of why he doesn’t just go back for her later is never really satisfactorily addressed on-screen, though Terrance Dicks has a go in his novelisation of The Face of Evil.)
This is the situation that persists throughout most of the second half of the original run – companions are there out of choice, not just hitching a ride until they can get home. Not necessarily a choice the Doctor is initially on-board with, of course, which is why we get the Doctor’s justified complaint towards the end of Logopolis that he’s never chosen the company he keeps – other than the robot dog and the naval surgeon, all of the companions who first appear in the fourth Doctor’s era are foisted on him to some extent.
The first season of the fifth Doctor in many ways is looking over its shoulder at the very early days of the programme, and this includes both the number of regular travellers – a mighty four, and the format almost audibly creaks when it tries to accommodate them all – and to some extent their motivations. Adric and Nyssa are both aliens, unable to return home for different reasons, but Tegan is a human who really wants to get home (she’s got a job to go to). Obviously, this coincides with the TARDIS intermittently proving awkward to steer – although, of course, when the plot demands it the Doctor, and even other characters, can arrive on-time, on-target at the first attempt – which is why it’s a whole season before Tegan gets back home. At which point, though it’s not immediately apparent, she decides that home is rather less fun than TARDIS travel (the 70s dynamic reasserts itself).
The fifth Doctor’s era has been much analysed (and occasionally criticised, even by its star) for its attempt to do more interesting things with the regular cast – arguably for the first time, a proper companion meets the Grim Reaper, there’s an ‘evil’ companion, a robotic companion, a companion who’s a marketing gimmick, and so on. Despite this, the majority of the actual departures are fairly routine, although by this point most of them are not quite what you’d call voluntary: Nyssa leaves out of a sense of moral duty, while Tegan decides she’s had enough of all the slaughter and walks away. This is almost played as if it’s a spur of the moment decision she begins to regret nearly immediately, but, given the nature of the show at the time, it hasn’t been foreshadowed or built up to in any way. It would be interesting to see the modern series handle an idea like this – a companion walking away in disgust – but I can’t imagine it ever happening.

That cussed Kamelion.
Perhaps the oddest and most frustrating way a companion is handled is the treatment of Kamelion, who gets an arrival and a departure but doesn’t appear in the intervening five stories. Given the very iffy nature of the Kamelion prop this is hardly surprising, but anyone missing the second episode of The King’s Demons would be blissfully unaware that the TARDIS now had four occupants. The decision to write out Kamelion is, once again, unsurprising, but the way it’s done is startling to say the least – rather than having the android sacrifice himself in order to foil the Master’s schemes or save the Doctor, he gets critically damaged in the course of the plot and winds up pleading with the Doctor to put him out of his misery. Which he does. With the Master’s gun.
Quite why Kamelion qualifies for such horrendous treatment is not clear, though one inevitably detects the gory hand of Eric Saward at work behind the scenes – no ‘normal’ companion would be disposed of so brutally, nor, surely, K9, Kamelion’s closest analogue (prop, punning name, etc). It’s hard not to conclude that despite all the evidence to the contrary, Kamelion is really just a companion in name only.
From this point on in the original run, we get companion departures which are peculiarly muted and arbitrary (one gets the impression that Turlough leaves out of a sense of personal obligation more than any real desire to go, and Mel’s departure is so inexplicable that there’s a popular theory that she’s surreptitiously hypnotised into going by the Doctor), or… Well, here we come to the departure of Peri, which on paper looks like the result of Eric Saward having eaten too much cheese – initially she gets her mind completely wiped, and is then shot dead by Brian Blessed, only for the audience to learn a few weeks later that actually she’s fine and the two of them have shacked up together.
(Whether you go with the majority view that Peri went off with Yrcanos to be queen of Krontep, or – like me – find the idea of her taking Yrcanos back to the States to be an all-in wrestler rather more fascinating, this is surely the most absurd example of a companion being married off in the entire history of the show. The total lack of chemistry between, say, Andred and Leela is barely an issue set next to a relationship based entirely on sweaty-handed lust on his part and panicky avoidance on hers.)
Peri’s departure is at least supposed to serve as some kind of story point, in terms of the development of the Doctor’s trial – although you have to put your head on one side and really squint to discern this – but overall, one gets the impression that 80s production teams were treating the refreshing of the companion role as a routine part of the series’ format, not requiring any particular thought or care. Things may well have proven different if the series had continued for another year and Ace had received the departure we are told was in the works for her (being sent off to Gallifrey to become a Time Lord), as – whatever the shortcomings of Andrew Cartmel’s approach to storytelling – he did treat characterisation and character development with due importance. As it is, a combination of factors, not least of them the untimely death of Elisabeth Sladen, leaves the path between our last sight of Ace on Perivale Common and her reemergence as a charitable entrepreneur shrouded in mystery.

This never actually happened, apparently. But it’s probably Gary Gillatt’s fault anyway.
Companion departures these days are handled with a good deal more thought; in fact, one sometimes gets the distinct impression that the showrunner thinks up the departure first and writes the rest of the stories to lead up to it. But then, the programme itself is a subtly (and sometimes not-so-subtly) different beast these days, as we shall see.
I’m really enjoying your Dr.Who essays in particular.
I hope “But then, the programme itself is a subtly (and sometimes not-so-subtly) different beast these days, as we shall see.” leads to some more!
Don’t worry, this was always intended as the middle installment of three – hopefully part three will appear at some point over the holidays! Thanks for reading and commenting.
Which is your favourite? For me, even though she isn’t my favourite companion, Tegan had a brilliant exit.
Well, in terms of ones where it actually has some emotional impact and isn’t just an obvious piece of housekeeping, you’re quite limited. I think Jo, because it’s so carefully written and set up throughout the story. I like the *idea* of Tegan’s departure, but there’s so much slaughter in early 80s Who you wonder why this occasion in particular drives her into going. Possibly because she’s already home.