Neokalus Burr is the killer in Babysitter Bloodbath, and a stand-in for Michael Myers from Halloween. He's also the player character of Sanitarium Massacre.
He's an escapee of Lincoln State Sanitarium, and invades the home Sarah is babysitting at. He kills Jack with a screwdriver before moving in on Sarah. Sarah manages to gun him down with a revolver, but by the time the authorities arrive, his "corpse" is long gone.
In Sanitarium Massacre, the lore has Burr gunned down by police in a home invasion and locked up in a mental hospital for 8 solid years, before snapping, escaping his cell, and wreaking havoc upon the staff with his butcher's knife. It's very possible that this game serves as a prequel to Babysitter Bloodbath, and that Burr preyed upon Sarah after finishing up his massacre of his hospital.
He's a towering hulk of a man in a red boiler suit, black gloves, and a white clown mask. He's white, has short brown hair, and wields a kitchen knife.