Patrick Jane (Simon Baker)
The series protagonist and the Mentalist of the show. He had earned a living as a psychic but after series antagonist Red John murders his wife and daughter in retaliation for Jane's mocking, Jane admits he was a fraud and works as a police consultant for the California Bureau of Investigation. Though a bit eccentric, he is very perceptive and much of what he finds helps solve the cases they are investigating. He is very brilliant and in-tuned to what is around him, but is often cocky, playful, and annoyingly right, all characteristics that earn him friendship in each of his colleagues.
Teresa Lisbon (Robin Tunney) 
She is the team leader. Though Patrick often annoys her with his unusual behavior and going behind her back, she views him as an invaluable member of the team and will back him up on some of his most unusual theories. Her mother was killed in a drunk driving accident, leaving her father as an alcoholic, no other family members are mentioned. She is also the only member of the team he trusts with details of his past and they work well together, despite his attitude often causing her problems with local law enforcement.
Kimball Cho (Tim Kang)
Often portrayed as Jane's "right-hand man" he seems the closest to Jane, often requesting help regarding finding evidence, though he does get annoyed with Jane's habit of not telling him everything he knows concerning a case. He has a dry sense of humor and is shown to be friends with Rigsby.
Wayne Rigsby (Owain Yeoman)
Arson specialist, he develops strong feelings for Grace Van Pelt, causing him to be overprotective of her, though he does not act on them as it is against regulations. He is tall and buff, and a good friend to Jane, though, like the others, is often annoyed by his ways. He is shown to have a good friendship with Cho.
Grace Van Pelt (Amanda Righetti)
The newest member to the CBI. She has a deep belief in religion and psychics and will butt heads with Patrick every time he dismisses it or does something she sees as morally or religiously inappropriate. Certain episodes have shown her returning Rigsby's feelings but she too, will not act on them due to regulations. She is very strict, organized and a bit high strung, but is over-all a very valuable addition to the team.
Red John
The unseen antagonist of the series. Patrick has stated that "Red John" sees himself as a "showman", as he always makes sure that his trademark, the smiley face drawn with the victim's blood, is the first thing one sees before one sees the body. After mocking Red John on a talk show, Red John retaliates by killing Patrick's wife and daughter. Though only focused on three times during the first season, he is portrayed to be very intelligent. For instance, Red John hacked into the CBI's computer system and has been using the system to monitor them for some time. So far he has been known to have two accomplices, a man that has been mentioned to have died in prison and his son who held Red John in high regards. However, Patrick states Red John doesn't have partners, he has tools.