Warning: SPOILERS ahead for Halloween
In David Gordon Green's Halloween, Michael Myers (James Jude Courtney) escapes from a bus carrying inmates from one psychiatric facility to another - and we're pretty sure it's his own psychiatrist, Dr. Sartain (Haluk Bilginer), who's responsible for his escape.
At first glance, Dr. Sartain seemed like a straight-forward successor to Donald Pleasence's Dr. Loomis, who appeared in five of the previous Halloween movies. However, while Loomis came to the conclusion that Myers was pure evil, Sartain has a far more sympathetic view, and is openly dismayed by the decision to move him to a far less comfortable institution. We find out just how sympathetic Sartain is towards the end of the movie, when he kills Deputy Hawkins and pulls on Michael's mask - hoping for his own taste of Michael's evil.
Dr. Sartain's love of Michael Myers doesn't save him from the unstoppable killer - in fact, he gets one of the goriest deaths in the movie. After Sartain drives an unconscious Michael to Laurie Strode's house, Michael repays the favor by stomping on Sartain's head, instantly crushing it. Curiously, though, Michael didn't take the opportunity to kill Sartain earlier in the movie, when he escaped the bus. Though it's not stated explicitly in the movie, it seems likely that Dr. Sartain was personally responsible for setting Michael free.
Michael Myers actually makes a few interesting choices about who to kill and who to spare in Green's movie. After the bus crashes, he doesn't harm Dr. Sartain and he also doesn't harm any of the other patients. Later in the movie, as Michael goes steadily through the neighborhood slaughtering people in their homes, he kills a woman but then decides not to kill her baby, who is lying in a crib in the living room. When asked about Michael sparing the baby, Green joked that he did so because killing a baby "would be so rude."
Based on Dr. Sartain's attachment to Michael, his ominous promise to stay by Michael's side during the transportation, and his eventual heel turn, it seems likely that Sartain either set Michael free on the bus and then allowed him to cause chaos, or caused the bus crash himself and set Michael free afterwards. Rather than being grateful for the assistance, Michael likely spared Sartain because he perceived him as equal in insanity to the other patients on the bus. However, wearing Michael's mask and then trying to imitate him was just plain rude, so naturally the doctor had to go.
It's a shame that Bilginer's character doesn't get more screen time in Halloween, because while we know he has a sick fascination with Michael, we never really get to take a proper look inside his head. Well, not figuratively, anyway.