Way before the campy comedy aspect started getting played up, the Child's Play movies were actual horror.
Child's Play is about a murderer named Charles Lee Ray who is killed by police in a shootout at a toy store, but not before a magical lightning bolt sends his mind into a Good Guy doll. He is soon bought and given to Andy, a little kid with a single mom and some issues of his own. Once Chucky (the doll) starts killing people like Andy's nanny and an old enemy of his, the police suspect Andy of being insane. To make matters worse, Chucky needs to possess the first person he "came out" to and that is Andy, also.
You have to know that, when this movie came out, we were only a year or so into the national nightmare known as My Little Buddy. These dolls were the same size as the kids they were aimed at and the gimmick was that they talked to you. There is a famous scene in this movie where Andy's mom figures out she never put batteries in the damn thing but it has been talking up a storm. I think that was a pretty common fear. Despite the innate creepiness, the filmmakers had an uphill battle making a little toy into a legit threat but they made it work. A kid-sized doll with a butcher knife and movement skills can be formidable.
Later movies got into Chucky's love life and spawn but this is where it all began.