Hal Mason is a main character in the first, second, third, fourth, and fifth seasons. He's a scout for the 2nd Massachusetts Militia Regiment and the first of its members to discover the Espheni Overlords. Hal was in a relationship with Karen Nadler, and after she was captured by the Espheni he started a relationship with Margaret and eventually married her.
In season three he was under the aliens' influence after having a parasite injected in him by Karen through a kiss. Karen's probe affects him deeply; he thinks he is meeting her in his dreams, but in reality, he is meeting her at night to tell her his father's plans, and Hal is thought to have become paralyzed losing the ability to walk. Later in season 3. the doctors at Charleston, with the help of the Rebel skitters remove the bug from him.
In season four, Hal is his father's second-in-command, leading the ghetto resistance while Tom is held in solitary confinement and befriends a Volm, Shaq.
