Which movies, books, TV series, ANYTHING, talk about a serial killer that ends up, well, killing ALL the human beings on this Earth one by one?

Yes, you heard me. They might take hundreds of years, or something like that. If you want rebut that they give birth to other individuals, then add the infertility trope of entertainment. In any case, use your imagination. The only thing that matters is the staple of a serial killer of the whole humanity.