Dr. Daniel "Dan" Challis is a main protagonist of Halloween III: Season of the Witch and is played by Tom Atkins.
He is a hardworking doctor struggling with the relationships between him and his ex-wife, Linda, as well as his children, Bella and Willie. On October 23, a man named Harry Grimbridge is brought into the hospital where Dan works, trembling with fear and clutching a jack-o'-lantern mask. Harry is killed that night by an unidentified man who then goes to his car and immolates himself. The next day, Dan is confronted in a bar by Harry's daughter, Ellie. He tells her about the strange events of the night before and shows her the mask her father was holding when he was admitted to the hospital.
Along with Ellie, Dan traces the mask back to Silver Shamrock Novelties, a company based in the town of Santa Mira. While in Santa Mira, Ellie mysteriously disappears and Dan is captured by Conal Cochran's android henchmen. Dan discovers Cochran's plan to kill millions of children on Halloween night using his masks. He finds out that the Silver Shamrock trademarks on every mask contain a computer chip and a small fragment of Stonehenge. On Halloween night, a television commercial will air activating the computer chip causing the mask wearer's heads to dissolve and erupt with insects and snakes. Cochran shows this to Dan in a demonstration, in which he kills a family.
Dan eventually escapes captivity in Cochran's factory and rescues someone he believes to be Ellie. He destroys Cochran and the factory by dumping the Silver Shamrock trademarks throughout the building and airing the commercial which will activate the computer chips inside. However, when he is returning home, he is attacked by the android which he thought was Ellie. After an intense fight, he kills the android with a tire iron and runs to a nearby gas station where he tries to convince the station managers not to air the Silver Shamrock commercial. He persuades them to take it off channels one and two, but not channel three. At the end of the film, he is seen yelling, "Turn it off! Stop it! Stop it!", although it is seemingly too late for him to prevent the computer chips being activated.