Michael Myers is a fictional character from the Halloween series of slasher films. He first appears in 1978 in John Carpenter's Halloween as a young boy who murders his elder sister, Judith Myers. Fifteen years later, he returns home to Haddonfield to murder more teenagers.
Vote which fictional character would naturally fit in-universe with a big-named franchise! No time-travel, no interdimensional crap, no "Pooh's Adventures", they would just exist in-universe.