Ben Mears kills Susan Norton by driving a stake through her heart after Barlow turns her into a vampire.
In Stephen King’s 1975 novel ’Salem’s Lot, Susan is Ben’s romantic partner and one of the town’s central victims. After her transformation, Ben is forced to confront the woman he loves as an undead predator rather than leave her to attack others.
The scene is especially tragic because Susan is not killed by Barlow himself, nor by Mark Petrie, Matt Burke, or Jimmy Cody. Those characters are involved in the group’s fight against the vampire infestation, which makes the names easy to confuse. Ben also helps destroy Barlow, but Susan’s staking is a separate act.
Adaptations retain the basic outcome, though details and timing vary. In the 1979 miniseries, Ben stakes Susan during the later confrontation, while other film and television versions rearrange events. The canonical answer to the book-based question remains Ben Mears.