Thomas J. Crapper.
He didn't invent the toilet. He only made it popular and modern.
To all you guys that said nukes, really? Did anyone even read a scientific magazine before? Pretty much any destruction power in the galaxy is a lot stronger then the nuke.
-Anti-matter (could make an anti-matter bomb) 1 gram of anti-matter exploding = I think it was 100 000 times the strength of a nuke.
-Supernovas or ultranovas are like H bombs but a billion times stronger.
-Obviously black holes are one of the most "destructive" (if you consider it destructive) things that we know of.
-Impacts of huge objects like a meteor(diameter of 10km) hitting the earth would cause an explosion 10 000 times bigger then all the nukes that we have combined.
-Gamma immersions from the supernova explosion would kill all life form.
-Somebody that creates a deadly virus that can spread really quickly could also cause many more deaths then a nuke.