Alexandra Forrest
Alex is an extremely successful editor with a publishing company, an obviously capable and motivated woman whose workplace behavior has never hinted at any degree of dysfunction or instability. When she meets Dan Gallagher through business connections she realizes that he shares the same instant physical attraction that she is feeling and is not surprised when the two sleep together. It soon becomes apparent, though, that she has taken the affair considerably more seriously than Dan has. This may also indicate that she views infidelity more seriously than he does also; for Dan it is a mistake never to be repeated that he will sweep under the rug as though it never happened. For Alex it is a sign that he is not committed to his marriage and absolute proof that she is a better fit for him than the wife he has cheated on.
Alex is wildly obsessive about Dan, lacking control and behaving in a very impulsive manner. Psychiatrists have used the film as an illustration of borderline personality disorder. Alex is terrified of abandonment and her efforts to avoid it become increasingly frantic. She suffers from sudden and extreme bouts of anger and does not generally direct this anger at the person who has hurt her but turns it inward or transfers it to the person she feels that Dan is abandoning her for. Alex will often self-harm and early in the film we see her slashing her wrists. It is likely that she uses "cutting" as an emotional outlet which might explain why she has apparently kept her obsessive tendencies in check until meeting Dan.
Dan Gallagher
Dan is a successful New York attorney who appears to have the Anerican dream. He loves his job and is respected in the workplace. He has a wife who adores him and a beautiful daughter whom they both adore. However Dan also seems to be a person with wavering moral fiber and a lack of self control. When he meets Alex the attraction he feels for her prompts him to be unfaithful to his wife. The ease with which he does this indicates that he has cheated in the past and managed to get away with it; the ease with which he is able to put the tryst behind him without much thought also suggests this.
Dan is somewhat of a pleasure-seeker but extremely out of his depth walking through the psychological minefield that is Alex Forrest. When Alex tells him she is pregnant he goes straight into disaster management mode rather than wondering about the validity of her claim.
Dan does not take responsibility for either his actions or their consequences; when he learns that Alex is pregnant he wants nothing to do with the child and will not take responsibility as a (possible) father. Similarly he would prefer to get a restraining order against Alex, putting one hundred per cent of the blame on her, rather than admitting to his wife that he has been unfaithful. Although Dan is cast in the light of victim along with his wife he is not entirely blameless and was equally culpable as Alex in the initial affair.
Beth Gallagher
Beth is also a very strong woman, not the force in the workplace that Alex clearly is, but a practical, feisty force nonetheless. Beth's prime motivation is the protection of her daughter, Ellen, and her warning to Alex that she will kill her if she comes near them again is genuine and also prophetic. Much of the power in the film belongs to Beth. It is she who tells Dan to leave when he admits his affair; he does not willingly leave her. It is also Beth who decides when he should come home again, astutely judging that they are all safer together rather than separately where Alex can overpower them one to one. The decision to allow him to come home again illustrates her protectiveness of her daughter not only by keeping her physically safe but also by making sure Ellen's family remains intact.
The power also transfers to Beth at the end of the film when she is the one who kills Alex.
