Sir William McCordle (Michael Gambon): The rich asshole who gets murdered. We don't blame whoever did it. Husband to Lady Silvia.
Constance, Countess of Trentham (Maggie Smith): A snobby, useless old lady who is at least partially financially reliant on Sir William. She attends the hunting weekend because she worries that Sir William is going to cut off her allowance, but he is murdered before that happens.
Lady Sylvia McCordle (Kristin Scott Thomas): Sir William's wife. Very haughty and icy, even to her own daughter. Became married to Sir William by "cutting cards" with her sister Louisa for the right to marry him. It becomes very obvious that they weren't meant for each other. Ends up owning Gosford Park.
Isobel McCordle (Camilla Rutherford): Daughter of Lady Sylvia and Sir William. Apparently has "done something" with Mr Nesbitt. Gigglesome friends with her maid, Elsie.
Lady Lavinia Meredith (Natasha Wightman): Wife to Commander Meredith and sister to Louisa and Lady Sylvia.
Lieutenant-Commander Anthony Meredith (Tom Hollander): Husband to Lady Lavinia. Is in financial ruin, and hopes to save himself through encouraging Sir William's investment in his Army supply business, an arrangement Sir William wants to back out of. Is responsible for a graze shot at Sir William the day of the hunting trip.
Louisa, Lady Stockbridge (Geraldine Somerville): Wife to Lord Stockbridge and sister to Sylvia and Lavinia. Lost the privilege to marry Sir William to Sylvia, but it's pretty obvious that they're having an affair.
Raymond, Lord Stockbridge (Charles Dance): Louisa's hard of hearing husband. Sylvia makes a few passes at him, but he's too indifferent to her to accept.
The Hon. Freddie Nesbitt (James Wilby): Husband to Mabel. Married her for her father's money. It's all gone now, and he clearly despises his wife. More than likely has had some "thing" with Isobel.
Mabel Nesbitt (Claudie Blakely): Wife to Mr. Nesbitt. Comes from a working class family, so the aristocrats hate her.
Lord Rupert Standish (Laurence Fox): Has no relation to anyone here. Was apparently invited to court Isobel, but Isobel breaks it off after over-hearing Mr. Blond say to Lord Rupert that he can do better than Isobel, because it would be too long to get his hands on the McCordle money, now belonging to Sylvia.
Jeremy Blond (Trent Ford): Friend of Lord Rupert Standish. Is discovered by Mary having sex with Bertha in the scullery.
Ivor Novello (Jeremy Northam): An actor who arrives with Weissman and Denton. He takes it upon himself to entertain the rest of the guests by playing the piano and singing in the drawing room after dinner.
Morris Weissman (Bob Balaban): A Hollywood producer researching British contry living for his new film, which is also a whodunnit set in a large country house.
Jennings (Alan Bates): Sir William's butler. Was a WW1 deserter and conscientious objector. Is an alcoholic.
Robert Parks (Clive Owen): Lord Stockbridge's valet. Raised in an orphanage outside of London. Is the illegitimate child of Sir William and Mrs Wilson. Takes the opportunity to stab Sir William, but isn't actually the murderer, if you can get your head around that.
Mrs. Elizabeth Croft (Eileen Atkins): Gosford Park Head Cook. Bitter rivals with Mrs. Wilson and is also her sister. She had an affair with Sir William when she was young and working in his factory, along with her sister. She became pregnant but the baby died in infancy. Mrs. Wilson gave Parks up, which is the source of the tension between her and Mrs. Croft..
Henry Denton (Ryan Phillippe): An actor posing somewhat unconvincingly as the manservant to Mr Weissman in order to research a role. Becomes the servants' Butt-Monkey upon revealing his identity. Sleeps with Lady Sylvia, though she loses interest when he reveals himself as an 'upstairs', and is likely sleeping with Weissman too.
Elsie (Emily Watson): Head housemaid. Is one of Sir William's lovers, an indiscretion she lets slip while waiting table at dinner one night. Friends with Isobel.
Mrs. Wilson (Helen Mirren): Gosford Park Housekeeper. Murders Sir William. She realises that Parks had discovered Sir William was his father, and that he probably wanted to kill him. So she poisons Sir William first, thereby stopping Parks from committing murder - you can't murder a corpse.
Probert (Derek Jacobi): Sir William's valet. Is devastated by his master's death.
Miss Mary Maceachren (Kelly Macdonald): Lady Constance's Naïve Newcomer ladies-maid. Is, arguably, the main character and acts as Audience Surrogate. Finds out both Parks and Mrs. Wilson. Is also Lady Constance's gossip collector.
Dorothy (Sophie Thompson): Gosford Park still-room maid. Is clearly in love with Jennings.
Lewis (Meg Wynn Owen): Lady Sylvia's lady's-maid. So loyal it's annoying.
Arthur (Jeremy Swift): Another footman. Implied homosexual. Probably for this reason, he really wants to be chosen to dress Mr Novello. Or he might just be a very big fan.
Barnes (Adrian Scarborough): Commander Meredith's valet. Overhears Commander Meredith saying that he was glad that Sir William died because his investment in now secure. He then proceeds to rat him out.
Bertha (Teresa Churcher): A kitchen maid.
Inspector Thompson (Stephen Fry): The bumbling detective who comes to investigate the murder. Discounts the possibility that anyone below stairs may be the murderer: he's interested only in those upstairs as they might "have a real connection" with the victim.
Constable Dexter (Ron Webster): Assistant to Thompson. Clearly much more competent. To the point perhaps the only reason why he's not the Inspector is because the Constable is working-class and the Inspector is rather more middle-class.
Pip (Kiki - Griffon Bruxellois): Sir William's lap dog. Sir William obviously loves the dog above anyone else in his family except Lady Stockbridge. The dog is the unwitting bane of the servants and Lady Sylvia hates it. Elsie ends up keeping it.