Halloween's opening scene — in which the violent murder of Michael's older sister, Judith, plays out visually from Michael's perspective — made cinematic history. When the movie came out in 1978, it was unheard of to film a profoundly unsettling, graphic murder from a second-person perspective. Its effects were unparalleled, though, as putting the audience in the shoes of a heartless murderer forced them to empathize with him. Yet, as bone-chilling as the scene was, it was the reveal of who committed the murder that left moviegoers gasping.
After the violent murder, the film pulls us out of Michael's perspective, and we see his parents discover him, just 6 years old, wielding a butcher knife. No more than a child, it's hard to stomach the reality of what we're seeing. How could a child commit such an atrocious act, and for what reason?
Michael is swiftly taken into custody and hospitalized in Warren County's Smith's Grove Sanitarium, where he remains for the next fifteen years. At this point, he escapes from the sanitarium and returns to his childhood home — the fictional town of Haddonfield, Illinois — and stalks Laurie Strode and her friends, picking them off one by one until his final confrontation with Laurie.
Due to Michael's first kill being at such a young age, followed by hospitalization for most of his life, we don't get any insight into his mental state or any insight into his personality. He also doesn't speak. He seems to have one motivation in life, and that's to kill for unfathomable reasons. Due to the elusive nature of his character, many people refer to Michael as "The Shape" in canon — more of being of pure evil than an actual person. Most would describe Michael as a boogeyman, with no real identity beyond that.