I won't mention the name, but there's a chain grocery store that moved into my area a few years ago and has blown the competition away. I guess you would call it a category killer. The prices are at least half of what other mainstream grocery charge, but the quality is just as good. It's not one of those low-end grocery store chains that buys the cheapest off-brands available. They contract with name brand food companies to make a similar product at a lower retail price.
I think once people shop at this particular grocery store chain a few times and get used to the no-frills aspect, they stop doing most of their shopping elsewhere. It doesn't offer everything a shopper might want, but I'll bet it covers about 80% of a person's average shopping needs. I think this store would be considered a category killer in the retail grocery field.