Here is a list of the main cast and characters on the Showtime series Dexter.
Michael C. Hall as Dexter Morgan (Seasons 1 - 6)
Dexter is a nice guy and borderline neat freak who works as a blood splatter expert for the Miami police department. No one would ever suspect that he's also a serial killer. He suffered extreme mental trauma as a child, leaving him with a stunted ability to feel emotion and an overwhelming desire to kill. His adoptive father, Harry, recognized the homicidal tendencies in the young boy, but instead of institutionalizing him, he helped Dexter control his urges and hone them for a more noble purpose: killing only people who've gotten away with murder due to holes in the judicial system.
Jennifer Carpenter as Debra Morgan (Seasons 1 - 6)
Debra is Dexter's sister. She's also a police officer who works with him in the homicide division. She's a foul-mouthed, tough-as-nails tomboy who nonetheless has a desperate need to feel loved. She falls in love quickly with men who never turn out to be "the one," a legacy of failed relationships traced back to the fact that she feels her father favored Dexter when they were kids.
Julie Benz as Rita Bennet (Seasons 1 - 4)
Rita is Dexter's girlfriend, a mild-mannered single mother of two who takes comfort in Dexter's stability, in light of her ex-husband's drug problem and incarceration. She has no idea about Dexter's dark side; the worst she suspects is that he might have a substance abuse problem.
James Remar as Harry Morgan (Seasons 1 - 6)
Harry is Dexter's adoptive father. Although Harry died years ago, he plays a big part in Dexter's life, having taught him a moral "Code" of behavior for utilizing his sociopathic tendencies to punish the wicked. Dexter's frequent flashbacks to lessons taught by Harry shape his actions in the present.
Lauren Velez as Maria LaGuerta (Seasons 1 - 6)
Maria is Dexter's boss. She's exceedingly ambitious and not above sneaky tactics to help her rise up the ranks in the police department. That said, she has a heart and is loyal and supportive of her friends. She and Debra have a contentious relationship, but Dexter gets along fine with her -- as long as she doesn't discover his secret.
David Zayas as Angel Batista (Seasons 1 - 6)
Batista is Dexter's good-natured co-worker and the closest thing to a friend that he has. An honest and proud cop with a penchant for metaphysical philosophizing, he's also a caring family man who's trying to deal with the dissolution of his marriage.
Erik King as Sgt. James Doakes (Seasons 1 - 2)
Doakes is Dexter's co-worker and nemesis. He's a no-nonsense, by-the-rules cop with a sixth sense for crime, and he suspects that Dexter is up to no good. At the very least, he's just "weird." His weakness is his violent temper, which Dexter uses against him. LaGuerta, his ex-partner and only real friend in the department, tries to get him to calm down and ease up on Dexter.
C.S. Lee as Vince Masuka (Seasons 1 - 6)
Masuka works closely with Dexter in the forensics lab. He's a sex-obsessed science geek who's on good terms with Dexter and not-so-good terms with Debra, toward whom he makes constant (albeit playful) sexual innuendo.
Christian Camargo as Rudy Cooper (Season 1)
Rudy is Deb's Season 1 boyfriend. They have a whirlwind romance that culminates in Rudy asking her to marry him, but unbeknownst to her, he has a dark secret...
Jaime Murray as Lila (Season 2)
Lila is Dexter's Narcotics Anonymous sponsor. Although he doesn't have a drug problem, he uses her advice in dealing with drugs to help him deal with his addiction to killing. Because of this, he forms a deep emotional bond with her, seeing her as a kindred soul who sees him as he is. Of course, in reality, she doesn't know that he's a killer, and he doesn't know that she herself has a dark side.