Who is the first cereal killer on earth?

It's impossible to know who the "first cereal killer" on earth was, as there's no historical record of serial killing specifically targeting people who ate cereal.

The term "serial killer" implies a pattern of murder, usually with some psychological motivation. We don't have any historical evidence to suggest someone was targeting people for eating cereal in ancient times.

It's likely a humorous play on words, as "cereal killer" sounds like "serial killer," but it's not a real historical or criminal category.