Charlie is a successful and affluent 40 year old bachelor who has a career writing advertisement jingles. Charlie resides in a large oceanfront home in Malibu, California, and is portrayed as a chauvinistic, hedonistic womanizer; all he cares about is having sex. The pilot begins when his wimpy brother Alan becomes divorced from his wife, moves out of their house, and has to move in with his brother. Alan has shared custody of his son Jake (10 when the series began), who stays with him part-time. Though some believe the title is in reference to the fact that Jake is only with Charlie and Alan half the time, it's really referring to the fact that Jake isn't an adult yet, and only "1/2 a man".
Rose (Melanie Lynskey) is Charlie's zany neighbor and female stalker. Rose had a one night stand with Charlie shortly before the show started, which she believed to be more signficant, and tends to enter his house through the patio in the most inopportune moments, expressing her ambition of obtaining Charlie, and often serving as a good, albeit crazy, friend and adviser. Although obviously troubled herself, Rose has stated a few times that she has a Master's degree in psychology. In various episodes it is insinuated that Rose is very slowly orchestrating a psychological plan to win Charlie back. Early in the series after she's become "Scrabble" friends with Alan as a way to get closer to Charlie, she's heard to say (to herself) "Phase one, complete."
In one episode, Rose's father Harvey (Martin Sheen) asks Charlie of his intentions with his daughter after an apparent second one-night stand between the two. Harvey then meets Charlie's and Alan's mother and has an affair with her, stalking her and popping in just like his daughter does. We then learn from Harvey's mother that "that's what happens when you marry a first cousin," explaining Rose's family's dementia.
Many of the episodes feature Judith misusing her alimony (before she remarried and Alan no longer had to pay her) and child support (she got a breast enlargement in one episode with her alimony).
Another important recurring character is Berta (Conchata Ferrell), Charlie's sarcastic and sharp-tongued housekeeper. She trades insults with Charlie and it's clear the household can't function without her. She usually tolerates Alan as long as he doesn't make excessive demands for particular food products and often refers to him as "Zippy." Berta also enjoys occasionally starting trouble between the brothers by needling each one about the other while she sits back and watches the conflict take place.
Alan and Charlie's mother, Evelyn (Holland Taylor) is a hip, wealthy, early-sixties, many-times-divorced, probably bisexual, promiscuous, controlling mother of the brothers. Both Charlie and Alan attribute their life's problems to the dark manipulative force their mother manages to exert upon them even now, adding to the caustic humor of the show in the situations depicting their vain attempts to escape her. For all of her selfishness and manipulation, Evelyn does love her kids and grandson deep down.
Another recurring theme is the conflict of personalities between the two diametrically opposed siblings, the relaxed, good-life, woman-catching, commitment-phobic Charlie and the uptight self-conscious nerdy Alan. Alan can sometimes appear to be jealous of Charlie's lifestyle, and can sometimes try to stop Charlie's decisions. This also provides opportunities for comedy in the show, with Alan, having admitted defeat, making comments such as 'it's like talking to a horny chimp', or 'it's like trying to talk Shakespeare to a Hershey bar'. However, every season has had at least one episode where Charlie and Alan are seriously fighting with each other, although the conflicts are generally resolved by that show's end.
A great deal of the humor on the show comes from the real-life experiences of creator Chuck Lorre. In a now-famous Entertainment Weekly interview, Holland Taylor said that Lorre was using the memories of his own less-than-great relationship with his mother for the storylines involving Evelyn and Charlie/Alan. Charlie Sheen also said that it was "no accident...that Chuck finally decided to do a show about men. I'll leave it at that."