Dr. Edward George Armstrong is a successful Harley Street surgeon and also a recovering alcoholic at the beginning of the novel. He is accused of killing a patient, Louisa Mary Clees, while operating on her drunk. As the novel goes on, the remaining characters begin to suspect he is the killer after his mysterious disappereance, only for it to turn out that he became an unwitting accomplice in the judge's plan and ended up getting murdered by the judge himself.
William Henry Blore is a former policeman who tends to be a bit too bold for his own good. He is accused of causing the death of an innocent man named James Landor by planting false evidence and landing him in prison, which caused him to die of untreated tuberculosis in jail. In the game, this is anted up to give him a more personal connection to the character the player controls when it's revealed that he also framed the character's brother to take the heat off himself.
Catch Phrase: "I get it!" in the 1945 film version. And when it seems as though he really does get it, he gets it— on the head from a marble clock.
The 1989 adaptation takes this to a whole new level— not only is he Too Dumb to Live, he is also paranoid bordering on Ax Crazy. After discovering the body of the General, he actually tries to shoot Lombard.
Old Fashioned Copper: He predates the milieu associated with the trope (Britain in the 1970s), but he could be considered a precursor of it.
Emily Caroline Brent is a staunchly religious spinster who takes a cold, unforgiving attitude towards anyone who, in her eyes, is a sinner. She is accused of driving her pregnant servant girl, Beatrice Taylor, to suicide after throwing her out of her household. In the game, she is the murderer— Gabrielle Steele, who killed the real Emily Brent —her motive being to torture Wargrave by making him watch others die and being powerless to stop it because he sentenced her lover to death.
Psycho Lesbian: In most of the Harry Alan Towers adaptations, at least.
Why Did It Have to Be Snakes?: She hates, hates bees and wasps (in adaptations— in the novel she mentions quite enjoying honey and never brings up bees). And of course, U.N. Owen uses it to his advantage.
In the game, she states she's allergic to bees.
Vera Elizabeth Claythorne is a young former governess, now gym teacher and secretary. She is accused of causing the death of her young charge, Cyril Hamilton, by allowing him to swim out to sea and drown, which she vehemently denies. It turns out that she did do it so the charge's uncle Hugo, who was her lover, could inherit the child's estate. Said lover was the only one who found out, but by then Vera was cleared of all charges, so he crossed the Despair Event Horizon and turned into The Alcoholic. Vera is constantly tormented by memories of the ordeal, until it reaches the breaking point at the end, where she is faced with the choice to hang herself...and does so. However, this is averted in the play and game, where it was the uncle who killed the boy.
Anti-Hero: In all fairness, she is the closest thing to a main character we have as she outlives all the other guests.
Proper Lady: Mercilessly deconstructed and she becomes a...
Yandere: Less in the Hollywood adaptations, but very much in the book. Not quite as much in the Russian film adaptation, but a single flashback showing her coldly watching Cyril die after Hugo explains why he can't marry her is all it takes to seal it.
Philip Lombard is a cool-headed and intelligent man, once a mercenary having seen various parts of the world. He is accused of leaving twenty-one men from an African tribe to starve and freely admits to it.
Black Comedy: He loves bringing up the foreboding poem at the worst possible moments.
Death of the Hypotenuse: In the game if you choose not to save him at the end. Even if he lives, however, Vera will still end up with Patrick (assuming she's saved, too).
Even Evil Has Standards: He definitely has a chivalrous streak in the novel and Wouldn't Hit a Girl although since he got killed because of it, it could also be considered Death By Sexism. This is subverted in the Russian version, however; he comes across this way at first, or at least a bit protective of Vera. Turns out he had otherideas.
Gentleman Adventurer: What he is the Hollywood versions, although this can be attested to the character not really being Lombard. Novel!Lombard is more like a evil version of the trope.
I Want My Beloved to Be Happy: In the game, or more specifically in the game's best end, he lets Vera go with Patrick with the instruction to take care of her.
Politically Incorrect Villain: Besides his crime of course, it's kind of interesting that while the newer version of the novel replaced the racist earlier title, Lombard's anti-Semitic sentiments are left intact, and while his chivalry is a redeeming quality, it also marks him as sexist.
Spared by the Adaptation: Play and Hollywood adaptations. Depending on what you do in the next-to-last chapter of the game, you can either play this straight, or subvert it.
Then Let Me Be Evil: In the stage version, Lombard actually didn't leave his men to die but tried to save them in every way he could. However, the rumor spread that he had abandoned them, and eventually he got so tired of denying it that he decided to play along.
Wouldn't Hit a Girl: Played straight between him and Vera with disastrous results in the novel, ending in his death.
General John Macarthur is a retired World War I general. He is accused of causing the death of Arthur Richmond, his wife Leslie's lover by sending him on a mission that guarantees him dead.
Cassandra Truth: He predicts none of the guests will be leaving the island alive, but his ranting is first dismissed to him just being older and thus, more likely to be off his rocker.
Death Seeker: Because of his deep guilt over his actions, he takes on a fatalistic attitude toward the certainty of the guests being killed and seems to welcome death.
In a later Canadian novel adaptation, nothing happened to him because of this property. He then admits to the police that he killed the other nine people so they can hang him, but he can't explain the story.
May-December Romance: Implied among him and Leslie, which explains why she ultimately turned to a much younger man.
Uriah Gambit: His method of doing away with his wife's lover, in a neat inversion. He stays away from church whenever the passage about David and Uriah is to be read.
Anthony James Marston is a young, spoiled vain youth with little concern for others. He is accused of causing the death of two young children, John and Lucy Combes, by accidentally running them over.
It's All About Me/Lack of Empathy: He regards running over two kids as unlucky for him, because his license was suspended, and feels no guilt about it. U.N. Owen characterizes him as essentially an animal and kills him first- since he has no morals or empathy to speak of, he's the most "innocent". Owen can't terrorize him or make him face his guilt; he opts to put him down quickly instead.
Large Ham: Every actor who has portrayed his equivalent in the Hollywood adaptations. They all make sure his death scene is the most exciting thing to watch in the whole film.
Thomas and Ethel Rogers are the butler and maid who accomodate the other guests. They are accused of causing the death of their former employer, a rich spinster named Jennifer Brady, by withholding a vital drug so she'd die and they could inherit her money.
The Butler Did It: Lampshaded in the game: "Will it ring true this time? Did the butler do it?" In both game and book, he didn't. Unless you count the backstory, where he did do it.
Domestic Abuser: Rogers mentally dominated his wife Ethel and essentially forced her into causing the death of Ms. Brady.
Shrinking Violet: Mrs. Rogers, sorta. Especially after their crime is revealed; ever since then, she seems to be always at the verge of a breakdown. Which is mentioned as one of the reasons why she was killed first and given a more or less peaceful death: being poisoned while in her sleep.
Stiff Upper Lip: He continues to do his job even as the corpses start piling up.
Lawrence Wargrave is a retired hanging judge with a no-nonsense attitude. He is accused of deliberately sentencing an innocent man, Edward Seton, to hang. It turns out that not only was Mr. Seton truly guilty, the judge is also the murderer. He could hold a possible record for sweeping nearly every single category under the Gambit Index.
Gambit Roulette: Works ridiculously well in the book, but fails in the Hollywood adaptations.
Hanging Judge: Obviously although in a way subverted, since despite his relish in punishing the guilty (and, you know, becoming a Serial Killer), he would extensively research the cases before him and advise the jury appropriately to make sure innocent defendants weren't punished.