The Vogon Captain in charge of overseeing the destruction of the Earth, Prostetnic Vogon Jeltz is sadistic, even by Vogon standards. When not shouting at or executing members of his own crew for insubordination, Jeltz enjoys torturing hitchhikers on board his ship by reading his poetry at them, then having them thrown out of an airlock into open space.

Physically, Jeltz is described as being unpleasant to look at, even for other Vogons. Given that Ford Prefect describes Vogons as having "as much sex appeal as a road accident", one can only imagine how much worse Jeltz must appear. This may explain his disposition.

Marvin is the ship's robot aboard the starship Heart of Gold. He was built as a failed prototype of Sirius Cybernetics Corporation's GPP (Genuine People Personalities) technology.

Marvin is afflicted with severe depression and boredom, in part because he has a "brain the size of a planet" which he is seldom (if ever) given the chance to use. Indeed, the true horror of Marvin's existence is that no task he could be given would occupy even the tiniest fraction of his vast intellect. Marvin claims he is 50,000 times more intelligent than a human, (or 30 billion times more intelligent than a live mattress(see Zem)) though this is, if anything, a vast underestimation.

When kidnapped by the bellicose Krikkit robots and tied to the interfaces of their intelligent war computer, Marvin simultaneously manages to plan the entire planet's military strategy, solve "all of the major mathematical, physical, chemical, biological, sociological, philosophical, etymological, meteorological and psychological problems of the Universe except his own, three times over," and compose a number of lullabies. He seemed to find this last task the hardest, and only one, "How I Hate the Night", is known.

Zem is an affable, yet quite stupid, swamp dwelling mattress. The mattress flollops, willomies and glurries around Squornshellous Zeta and tries his best to cheer up Marvin the Paranoid Android, who became stranded on the planet after having one arm welded to his side and one leg replaced by a steel pillar (which turns out to be of immense importance). Because of his stupidity he has the same conversation with Marvin every day until the android leaves. After attempting to make conversation about the weather (Marvin: "The dew has fallen with a particularly sickening thud this morning... if I had teeth I would grit them at this point"), Marvin's life story, and the economy of Squornshellous itself, Zem offers that Marvin should be more mattresslike. Zem is also the sole witness to Marvin's abduction by the Krikkit war robots.

Also note that "Zem" is the name of all Squornshellous Zeta mattresses. As Zem puts it, "Some of us get killed... but we never know which."

Deep Thought is a computer that was created by the pan-dimensional, hyper-intelligent race of beings (whose three dimensional protrusions into our universe are ordinary white mice) to come up with the Answer to The Ultimate Question of Life, the Universe, and Everything. Deep Thought is the size of a small city. When, after seven and a half million years of calculation, the answer finally turns out to be 42, Deep Thought admonishes Loonquawl and Phouchg (the receivers of the Ultimate Answer) that "[he] checked it very thoroughly, and that quite definitely is the answer. I think the problem, to be quite honest with you is that you've never actually known what the question was."

Deep Thought does not know the ultimate question to Life, the Universe and Everything, but offers to design an even more powerful computer, Earth, to calculate it. After ten million years of calculation, the Earth is destroyed by Vogons five minutes before the computation is complete

Flexible and imaginative, Hactar was the first computer whose individual components reflected the pattern of the whole. Hactar is assembled and programmed by the Silastic Armourfiends, who then order him to assemble an "Ultimate Weapon." Hactar, receiving no other guidance from the Amourfiends, takes the request literally and builds a supernova bomb which would connect every major sun in the universe through hyperspace, thus causing every star to go supernova. Deciding that he could find no circumstance where such a bomb would be justified, Hactar builds a small defect into it. After discovering the defect, the Armourfiends pulverize Hactar.

Rather than being destroyed, Hactar is merely crippled. He can still manipulate matter, but even a simple item takes millennia to manufacture. Over æons Hactar moves and recombines to become a dark cloud surrounding Krikkit, isolating the inhabitants. Deciding that the decision not to destroy the universe was not his to make, he uses his influence to make them build their first space ship and discover the universe; he then manipulates them into the same rage which the Armourfiends possessed, urging that they destroy all other life; Hactar has reassembled the supernova bomb, this time in working condition.

After an incredibly long and bloody galactic war, Judiciary Pag banishes Krikkit to an envelope of "Slo-Time" to be released after the rest of the universe ends. At the end of the novel Life, the Universe and Everything, after his scheme fails, Hactar slips the cricket-ball-shaped supernova bomb to Arthur Dent, who then accidentally saves the Universe again by being an abysmal cricket bowler.

Ford is actually from a small planet somewhere in the vicinity of Betelgeuse, and had originally only come to Earth to do some research for an article he was writing on it for the Guide.

Ford came to Earth for a week, and got stuck there for fifteen years, departing only when a fleet of Vogon constructor ships appear in the first episode, taking Arthur Dent with him. Ford is the source of much explanation of the weird universe that Arthur finds himself in; for example, the importance of knowing where your towel is, sticking a fish in your ear, and why the greatest cooks in the universe cook on Vogon spaceships. Ultimately, however, his personal mission is to find a nice party and get incredibly drunk.

Zaphod Beeblebrox is from a planet in the vicinity of Betelgeuse, and is a "semi-half-cousin" of Ford Prefect, with whom he "shares three of the same mothers". Because of "an accident with a contraceptive and a time machine", his direct ancestors from his father are also his direct descendants.

Zaphod is the inventor of the Pan-Galactic Gargle Blaster, a cocktail based on Janx Spirit. The series states that the effect of one "is like having your brain smashed out by a slice of lemon wrapped round a large gold brick." In the television series, two Gargle Blaster drinkers collapse in open-eyed unconsciousness after drinking while the spilled drink burns a hole in the floor; in the film, after the Guide is done explaining what the Pan-Galactic Gargle Blaster is and its effects, Ford and Zaphod yell in pain. The Hitchhiker's Guide to the Galaxy gives the recipe as follows:

"Take the juice from one bottle of that Ol' Janx Spirit.
Pour into it one measure of water from the seas of Santraginus V
Allow three cubes of Arcturan Mega-gin to melt into the mixture (it must be properly iced or the benzene is lost).
Allow four litres of Fallian marsh gas to bubble through it (in memory of all those happy Hikers who have died of pleasure in the Marshes of Fallia).
Over the back of a silver spoon float a measure of Qualactin Hypermint extract, redolent of all the heady odours of the dark Qualactin Zones.
Drop in the tooth of an Algolian Suntiger. Watch it dissolve, spreading the fires of the Algolian suns deep into the heart of the drink.
Sprinkle Zamphour.
Add an olive.
Drink...but very carefully."

The Guide also implies that there are multiple voluntary organisations available to rehabilitate those who would try the Pan-Galactic Gargle Blaster. Real versions of the drink have been made available at some stage shows of The Hitchhiker's Guide to the Galaxy, as well as bars such as Zaphod Beeblebrox in Ottawa, Ontario, Canada. Recipes for these "Earth versions" can be found at Wikibooks.[4] In an interview,[5] Douglas Adams stated that there are a number of environmental and weapons treaties, as well as laws of physics, which prevent the Pan Galactic Gargle Blaster from being mixed on Earth.

Tricia McMillan is a brilliant mathematician and astrophysicist whom Arthur Dent attempted to talk to at a party in Islington. She and Arthur next meet six months later on the spaceship Heart of Gold, shortly after the Earth has been destroyed to make way for a hyperspace bypass. The trilogy later reveals that Trillian eventually left the party with Zaphod Beeblebrox, who, according to the Quintessential Phase, is directly responsible for her nickname.

Along with Ford Prefect, Dent barely escapes the Earth's destruction as it is demolished to make way for a hyperspace bypass. Arthur spends the next several years, still wearing his dressing gown, helplessly launched from crisis to crisis while trying to straighten out his lifestyle. He rather enjoys tea, but seems to have trouble obtaining it in the far reaches of the galaxy. In time, he learns how to fly and carves a niche for himself as a sandwich-maker.

Slartibartfast is a Magrathean, and a designer of planets.[2] His favourite part of the job is creating coastlines, the most notable of which are the fjords found on the coast of Norway on planet Earth,[3] for which he wins an award. While trapped on prehistoric Earth, Arthur Dent and Ford Prefect see Slartibartfast's signature deep inside a glacier in ancient Norway.

When Earth Mk. II is being made, Slartibartfast is assigned to the continent of Africa. He is unhappy about this because he wants to make more fjords (arguing that they give a continent a baroque feel), and fjords in Africa would be hard for him to explain without natural glacial movement.

In any event, the new Earth is not required and, much to Slartibartfast's disgust, its owners suggested that he take a quick skiing holiday on his glaciers before dismantling them.

Slartibartfast later joined the Campaign for Real Time (or CamTim as the volunteers casually refer to it, a reference to CAMRA) which tries to preserve events as they happened before time travelling was invented. He picks up Arthur and Ford from Lord's Cricket Ground with his Starship Bistromath, after which they head out to stop the robots of Krikkit from bringing together the pieces of the Wikkit Gate.

When he first meets Arthur, Slartibartfast imparts the following wisdom on life:

Slartibartfast: "Perhaps I'm old and tired, but I think that the chances of finding out what's actually going on are so absurdly remote that the only thing to do is to say, 'Hang the sense of it,' and keep yourself busy. I'd much rather be happy than right any day."
Arthur: "And are you?"
Slartibartfast: "Ah, no. (laughs) Well, that's where it all falls down, of course."

The Lord is a cat, owned by The Ruler of the Universe. He might like fish and might like people singing songs to him, as the Ruler of the Universe isn't certain if people come to talk to him, or sing songs to his cat or even if the cat exists at all.

Agrajag is a piteous creature that is continually reincarnated and subsequently killed, each time unknowingly, by Arthur Dent.

Eventually, Agrajag becomes aware of his many past incarnations and wishes to take revenge on Arthur Dent, diverting his teleportation to a Cathedral of Hate. However, in the process of explaining his reasons for hating Arthur he mentions "Stavromula Beta," where Arthur ducks to avoid a shot fired by an assassin, which then hits Agrajag instead. Arthur, never having been to Stavromula Beta, has no idea what Agrajag is talking about, and Agrajag realises that he's brought Arthur to the Cathedral too early. Thus, any attempt by Agrajag to kill Arthur would be logically impossible. He tries to kill Arthur anyway, and once again dies at Arthur's hands while Arthur is defending himself, but not before setting off the explosives intended to kill Arthur by triggering a massive rockfall. Due to the laws of cause and effect and the laws of time and the universe (not to mention dramatic necessity), Arthur escapes the rockfall unharmed.

For the next few years Arthur travels the universe, secure in his knowledge that, no matter what happens, he cannot die at least until after he survives his assassination attempt at Stavromula Beta. In the novel Mostly Harmless Arthur's daughter Random Frequent Flyer Dent holds him hostage in a London club. When she fires her weapon Arthur dodges, causing the bolt to pass over his head and hit the man standing behind him. Earlier the victim (Agrajag) had dropped a book of matches which revealed the owner of the nightclub to be Stavro Mueller, and the name of the club to be Beta. Thus, what Arthur believed to be the name of a planet was actually the name of the nightclub, and Agrajag has died once again. Because of this, Arthur is now able to die as well, which, thanks to the Vogons, he does a few seconds later.

Hotblack Desiato is the ajuitar keyboard player of the rock group Disaster Area, claimed to be the loudest band in the universe, and in fact the loudest sound of any kind, anywhere. So loud is this band that the audience usually listens from the safe distance of thirty seven miles away in a well-built concrete bunker. Disaster Area's lavish performances went so far as to crash a space ship into the sun to create a solar flare. Hotblack is spending a year dead "for tax reasons".