1. Ed Gein
There's arguably no one man who's been more inadvertently influential to the horror genre than Mr. Edward Gein. Because of him, authors and screenwriters were inspired to create the following characters: Norman Bates in Psycho, Leatherface in The Texas Chainsaw Massacre, and Buffalo Bill in The Silence of the Lambs. But let's not give Gein too much credit here. After all, he was a murderer who also dug corpses out of graveyards and made trophies and other home-adorning paraphernalia from their bones and flesh.
In 1957, the Plainfield, WI, native confessed to a pair of murders, saying that he offed two local women over a three-year span. And when the authorities searched his home, they discovered a treasure trove of horror: human skin covering chairs, bowls made from skulls, four loose noses, the two victims' severed heads in bags, a belt made from female nipples, a lampshade made from a person's face, and 10 women's heads with the tops cut off, amongst other grotesqueries. OK, one more, for good measure: They also found nine vulvae snipped off and placed in a shoe box.
So, yeah, there's your Chainsaw Massacre connections. As for Psycho, it was later learned that, after Gein's abusive mother passed away, he started creating a "woman suit" (i.e., female skin taken from bodies that he'd tanned) so that he could give himself a makeshift sex change. Any questions about why Ed Gein takes the top spot here?