Played by Shiri Appleby. Liz Parker attends Roswell High School, where her favorite subject is science. Her best friends are Alex Whitman and Maria DeLuca. At the beginning of the series, she breaks up with boyfriend Kyle Valenti and engages in a dramatic relationship with alien-human hybrid Max Evans, which is the crux of the television series.
Played by Jason Behr. Max is an alien who arrived in the 1947 crah. Being a hybrid often forces him to hide his true self. Because he must conceal his true identity, Max is a complex character, very timid at times, yet passionate and carefree at others. Even before he knew that he was the clone of the king of Antar, Max emerged as the de facto leader among his friends.
Played by Katherine Heigl. Isabel Evans is an alien-human hybrid like her brother Max Evans and best friend Michael Guerin. Isabel is a very visible, popular girl at school. She hides her kind side beneath a front of haughtiness and cold unfeeling. On the outside, she is the most outgoing of the three hybrids and blends in with the human society with ease. However, deep down she craves stability and security, longing to fit in and be a "normal" girl like Liz or Maria.
Played by Brendan Fehr. Michael is the rebel and outsider of the group, even more so than Max and Isabel because he lives in a trailer park and suffers abuse from his alcoholic foster father, Hank. He becomes obsessed with finding out the truth about his origins as a means to escape the world that he has come to despise, and often acts in an impetuous way to achieve this goal. Michael is also the most emotional of the alien trio, and the one most likely to act on his feelings.
Played by Majandra Delfino. Maria is Liz's best friend, and is brought into the alien chaos early on. She has more trouble than Liz with accepting that Max, Michael, and Isabel are aliens. Maria is very involved in her music, especially singing. Eventually she and Michael become involved and are the most firey couple on the show, often fighting or breaking up. Their relationship proves to be special though as Michael stays on Earth for her.
Played by Colin Hanks. Alex is Liz and Maria's closest friend. He plays guitar and is generally considered to be fairly nerdy, but also funny and sweet. He loves Isabel before and after he finds out she's an alien. They have a brief relationship before Alex is killed by Tess, having been mindwarped into translating the alien book for her.
Played by Nick Wechsler. Kyle is used regularly as comic relief in serious situations. He has the most developed sense of humor of the group, and is always looking for the joke in a situation. He does, however, have a very serious and caring side, becoming very protective of those he cares about. Kyle's Buddhism is often used as joke fodder, with him often quoting philosophical texts to help in serious situations, to the exasperation of his father, Sheriff Jim Valenti, and friends.
Played by Emilie De Ravin. Tess came to Earth with the other alien-human hybrids, but left her pod after they left theirs. She was raised by another alien, Nasedo, who had apparently been sent to Earth to protect them. However, he had made a deal with Kivar 40 years before: return home with Max's son and deliver Max, Michael and Isabel to Kivar, who would have killed them. Tess becomes pregnant and leaves Earth, later to return to reveal the child is fully human. She gives up her life to protect it.
Played by William Sadler. Valenti is frequently the antagonist in the first season, albeit a sympathetic one. His father was also the sheriff of Roswell, and was ridiculed for his insistence that aliens live among humans. Valenti inherited from his father an old autopsy photograph from the 1950s of a body killed by inexplicable means, with a silver handprint on the chest. He becomes obsessed with discovering the truth about Max, but when he does he helps him instead of turning him in.
Played by Adam Rodriguez. Jesse is introduced in season three as Isabel's boyfriend, and later they get married without him knowing the truth about her being an alien. Jesse is a lawyer at Isabel's father's firm. When he finds out the truth about Isabel he finds it hard to cope, but by the end of the series is willing to stick by her. However, Isabel tells him she has to let him go, because it wasn't fair to drag him into everything without telling him.