- Lavinia Mannon: She is beautiful but she is not a feminine girl. She is the Mannon's daughter. She is 23 years old, and looked elder than her age. Her body is not interesting, and she always wears uninteresting clothes too. She’s looked bossy and talkative.
- Christine Mannon: A striking woman of forty with a fine, voluptuous figure, flowing animal grace, and a mass of beautiful copper hair. She wears green, which symbolizes her envy. Her pale face is also a life-like mask, a mask that represents both her duplicity and her almost super-human efforts at repression. Having long abhorred her husband Ezra, Christine plots his murder with her lover Brant upon his return from the Civil War.
- Orin Mannon: The Mannon son returned from war. Orin bears a striking resemblance to his father and Captain Brant, though he appears as a weakened, refined, and oversensitive version of each. He possesses a boyish charm that invites the maternal favors of women. He loves his mother incestuously, flying into a jealous rage upon the discovery of her love affair that leads to Christine and Brant's deaths. Orin will then force he and his sister to judgment for their crimes in an attempt to rejoin his mother in death.
- Brigadier-General Ezra Mannon: The great Union general. Ezra is a spare, big-boned man of exact and wooden movements. His mannerisms suggest the statue-like poses of military heroes. His brusque and authoritative voice has a hollow and repressed quality. As his near- homophonic name suggests, he is Agamemnon's counterpart, the general returned from war to be murdered by his wife and her lover. He continues to exert his influence in symbolic form. His various images, and his portrait in particular, call his family to judgment from beyond the grave.
- Captain Adam Brant: A powerful, romantic sea captain. Brant has a swarthy complexion, sensual mouth, and long, coal-black hair. He also of course bares a striking resemblance to the other Mannon men, sharing their same, mask-like faces. The child of the illegitimate Mannon line, he returns to wreak vengeance on Ezra's household. He steals Ezra's wife, a woman he imagines in the image of his mother, and seduces Lavinia to conceal their affair.
- Hazel Niles: A longtime friend of the Mannon children. Hazel is a pretty, healthy, dark- haired girl of nineteen. O'Neill describes her character as frank, innocent, amiable, and good. She functions as Orin's would-be sweetheart, and both Christine and Lavinia attempting to pass Orin off onto her so they can flee with their suitors. Hazel also haplessly attempts to rescue Orin from his fate.
- Captain Peter Niles: An artillery captain for the Union. Peter resembles his sister in character. He is straightforward, guileless, and good-natured, failing to apprehend the machinations afoot in the Mannon house until the very end of the trilogy. He functions as the suitor Lavinia first rejects and later takes up as a substitute for Captain Brant.
- Seth Beckwith: The Mannons' aged gardener. Seth is stoop-shoulded and raw-boned but still strong. Like his employers, his gaunt face gives the impression of a life-like mask. In his time with the Mannons, he has learned most of the family's secrets and colluded in keeping them. A watchman figure of sorts, he is repeatedly seen wandering the grounds and singing the sea chanty "Shenandoah."
- The place is at The Mannon house in New England, a harbor in East Boston.
- The time is in the summer, 1865–1866.
- Oedipus, it is tendency of the man who falls in love with a woman older than him, obsessed his mother character. Possibility since the man has little emotional closeness of a mother figure. The story showed this condition when Adam Brant fell in love to Christine Mannon and he is Christine’s lover, because Christine is Orin’s mother and she is elder than Brant.
- The Rival and Double, Orin became her mother’s rival because her mother has been sleeping with her husband, Brant, and because her mother also fell in love with Brant. In this condition Brant is double.
- Do not hurt our family.
- We should keep a good relation with our family.
- We should be patient when we face a problem.
- Do not be easy to vengeance to someone who hurt us.
- Do not betrayed our family.