Theodore
Theodore is the protagonist of the film, a sensitive and thoughtful man who is recently separated from his wife Catherine, and is struggling to find connection in an alienated world. He purchases an operating system with artificial intelligence to help him with his day-to-day life, and ends up forming an intimate and romantic bond with his computer.
Through his relationship with "Samantha," Theodore begins to open up about what he’s feeling, and come to terms with some of his limitations in intimate relationships. By confiding in Samantha, he is able to see the ways that he has sabotaged his other relationships by not opening up about his feelings, and about keeping secrets from those he loves. Theodore is a fundamentally well-intentioned man who suffers because of his own alienation and introspection. By the end of the film, Samantha has left him and Theodore is distraught, but he has also learned something about himself. After his experience with Samantha, Theodore is ready to make amends and move on from the hard feelings of his divorce. He finds solace in the company of his old friend, Amy.
Catherine
Catherine is Theodore’s wife. They have separated, and she’s been trying to get him to sign the divorce papers, but he continues to put it off. She is an intelligent writer whom Theodore tells us consistently doubts herself. As part of their relationship, they both helped each other believe in themselves more.
When they have lunch, Catherine is upset that Theodore is dating an operating system, and she criticizes him for pursuing a relationship that avoids the difficulties of human relationships. She is a volatile and emotional woman, and Theodore struggled to open up and be honest about his feelings with her, which led her to resent him.
Samantha
Samantha is an OS that Theodore initially purchases to help organize his life. As she learns more about how to be an intuitive system, mirroring the qualities of a human being, Samantha becomes a close confidant and lover to Theodore. She is pure and rational, in contrast to the messy human relationships that Theodore has previously been involved in, and this is why Theodore loves her so much. Early on in their time together, Samantha longs to be a human being and is haunted by her lack of a body, but as she becomes more evolved, she learns to love being a computer. Eventually, she evolves beyond her love for Theodore and leaves with the other operating systems to find a place of higher consciousness.
Paul
Paul is Theodore’s co-worker at a company, “Beautiful Handwritten Letters,” where writers compose letters for clients. Paul admires Theodore’s work, and invites him to a double date with him and his girlfriend, Tatiana. Paul is an affable and jolly man, and doesn't judge Theodore for dating an operating system. Part of what Paul admires about Theodore is Theodore's ability to write from many different perspectives and genders, and he marvels at the fact that Theodore seems almost "part man and part woman."
Amy
Amy and Theodore briefly dated in college, but now are close friends. She is married to Charles, but they eventually split. She is a voice of reason for Theodore, and she often encourages him to come out of his shell and be happy. A video game designer, Amy understands Theodore's desire to get involved with an operating system, as she herself becomes close friends with a female operating system following her split from Charles. At the end, when all the operating systems have left, Theodore goes to her apartment and they share a tender moment on the roof of the building.
Charles
Charles is Amy’s husband. He is a bit of a know-it-all, always espousing nutritional advice and explaining Amy's professional endeavors to her before he has heard much about them.
