Arthur Dent is the main protagonist of The Hitchhiker’s Guide to the Galaxy. He is an average Englishman of about 30 years old. Arthur is not particularly clever or remarkable and often comes across as nervous or confused.
Ford Prefect is Arthur’s best friend; he is a bit odd but is wryly humorous and intelligent. Although he blends into human society well, it is revealed that Ford is actually an alien of the Betlegeusian race sent to Earth to perform research for a book titled The Hitchhiker's Guide to the Galaxy. He was stranded on earth and couldn't hitch a ride until the Vogons came to destroy Earth. He accompanies Arthur on their adventures across the galaxy.
Zaphod Beeblebrox, Ford's semi-cousin, is a Betelgeusian and President of the Galaxy. He is incredibly clever and intelligent, but he also has trouble reasoning and is irresponsible, seeming to lack morals. He has two heads, three arms, and an awful taste in clothing. Although he is not a villain, Zaphod’s irresponsibility, stupidity, and other flaws seem to cause Arthur and Ford a lot of trouble when they arrive on his ship. He does not know exactly why he stole the Heart of Gold, but he muses that he possesses a secret that he cannot yet figure out how to access.
Trillian is a human woman from Earth whom Arthur met at a party and was interested in, but who then went with the charismatic Zaphod Beeblebrox instead. Zaphod easily convinces her to fly away with him on his ship. She does, however, grow to dislike Zaphod. She is very intelligent and approaches problems much more logically than Beeblebrox, or anyone else for that matter.
Marvin is a robot aboard Zaphod Beeblebrox's ship who is depressed and extremely pessimistic. He is often annoyed by Eddie, the name given to the ship's computer, due to its overly-cheery “personality.” Marvin has the brain the size of a planet and grumbles at his menial tasks.
The elderly and cerebral Slartibartfast is a Magrathean alien who helps to design planets. He won an award for designing the coast and fjords of Norway, and he also now works to create parts of Africa on the second version of Earth. He explains to Arthur the origin of Earth, as well as why Earth was destroyed.
A stupendous supercomputer (the second greatest computer in the Universe of Time and Space) built by a race of hyper-intelligent beings millions of years ago to give the Answer to life, the Universe, and everything. After seven-and-a-half million years the answer is 42, and Deep Thought says Earth will be the next supercomputer that can provide the Question to the Answer.
Mr. L. Prosser
The bureaucrat sent to Arthur's house with orders for the house to be bulldozed.
Prostetnic Vogon Jeltz
The grotesque leader of the Vogons who oversees the destruction of Earth and attempts to torture/eliminate the hitchhiking Ford and Arthur first by reading his poetry to them, then by sending them out into space.
The Heart of Gold's computer. Its personalities annoy Zaphod and Ford immensely; the first is a cheery one, the second a twangy matronly one.
Fook and Lunkwill
The first two programmers given the opportunity to turn on Deep Thought and ask it for The Answer.
Vroomfondel and Majikthise
Two philosophers initially dismayed that Deep Thought will put them out of a job. They are mollified, however, when Deep Thought tells them it will take 7.5 million years to come up with its response and that they can spend that time speculating.
Loonquawl and Phouchg
Two contemporary programmers given the opportunity to officially ask Deep Thought for its answer. They are dismayed to learn it is "Forty-Two" and that they now must seek The Question.
Frankie and Benjy
Two powerful mice (mice are some of the most intelligent creatures in the galaxy) taken from Earth by Trillion. Since the Vogons blew up Earth they did not get their Question, so they decide an easier way to get to it than commissioning a new Earth is via Arthur's brain.
The Hitchhiker’s Guide to the Galaxy Questions and Answers
The Question and Answer section for The Hitchhiker’s Guide to the Galaxy is a great
resource to ask questions, find answers, and discuss the novel.