Jerome, usually known as "J," is the narrator who lives and works in London.  He is taking a vacation along the Thames river along with two friends.  J. is confident and fairly jovial, always ready to exploit the funny failures of his two friends as he tells us, the readers, his story.  J. always makes himself seem better than his companions, he always seems to be "above" their immature antics.

George is one of the two friends who accompany J. on his trip along the Thames (for part of the time, anyway, due to his occupation). He is a banker who has a very strict time schedule and who is already ready for a pint after hours.  George is quite a character, always boisterous.  When he shows up for the vacation, he is sporting his wild style and carrying a banjo.  No one quite knows why George is carrying this ethereal banjo.  He can't play music.  Therefore, despite his quirks, J. still considers George quite boring except for his ability to find pubs.

William Samuel Harris is the other of the two friends who join J. on the vacation along the Thames.  J. finds William incredibly boring, lacking all "romance and poetry."  William is a lot like George in that they both like to plan their pubs and eats.  William also loves music, but has a horrible memory so can never remember the words to the comedy songs he loves so much.  There is one significant time on the trip along the Thames that William remains on the boat only to get exceedingly drunk.  William is also the one to propose the toast after they get off of the boat.  (Due to heavy rains, the three decide to take the train instead.)  "Here's to Three Men well out of a Boat!"

Montmorency, although a dog, is quite a character.  He is a crew member of the boat along the Thames.  J, George, and William swear continually that Montmorency is always fighting and would fight any other dog anywhere.  Ironically, the only thing that can make this dog retreat is a cat!  Apart from all this, Montmorency is always the most realistic of the four. 

The three main characters of the story are the narrator Jerome, generally known as J to his friends, and George and Harris. All are young and single.  Jerome throws in plenty of self-deprecating touches when talking about himself and also portrays his two friends in a humorous light. They all come across as somewhat lazy and awkward in many situations which gives rise to most of the comedy.Jerome comes across additionally as being quite romantic - he is always conjuring up pictures of the past while they journey along the river. George is the only one of the three depicted as actually having a job (he works in a bank) and is physically imposing, quite practical (he is the one who makes lists of what they should take on the boat, for example). Harris appears a bit more uncouth and hot-tempered than the others (for instance, flying into a rage when he can't get the drink he wants).

Provide full character sketches of all the characters in Three Men in a Boat.

J. is the narrator. If he has a “real” job, he doesn’t tell us what it is. He’s an avid storyteller who likes to add humor and exaggeration to every tale. He gets distracted by stories he’s reminded of, at every turn. He admits that he’s lazy. In Chapter XV, he famously says: “I like work: it fascinates me. I can sit and look at it for hours.” And yet, he seems to be the unofficial leader of this group of friends.

William Stanley Harris doesn’t seem to hold a “real” job, either. In today’s terms, we may consider him to be a high maintenance friend, and one who can sap everyone else's strengths, if given the chance. He’s confident that he can do certain tasks, and it eventually turns out that he can’t. In Chapter XI, he makes an unsuccessful attempt at cooking scrambled eggs for breakfast for the group.

George works at a bank. He has to work early on the first day of the trip, so J. and Harris have to pick him up en route. He seems to be more organized and focused than the other two friends; although at times, like them, he can become confused or clumsy. In Chapter XVII, he accidentally knocks down the mounted fish on the wall of the inn. But he does cook a good Irish stew in Chapter XIV.

Montmorency is the fox terrier who serves as the dog on the trip and in the book title. Looks can be deceiving. He looks like an amiable enough and mellow animal. But he likes to chase cats. He likes to bring dead things back to his friends. He likes to get in the way when people are busy with a complex task, as he does when the men are packing in Chapter IV. Here he is treated as a worthy fourth member of the group, however.