Best and worst could go to Fritz Haber. You may not have heard of him unless you're into agriculture, but he is a Prussian Chemist, born in 1868. He worked with Carl Bosch and created the Haber-Bosch process. This process allows you to synthesize ammonia from hydrogen and nitrogen. Large amounts of fertilizer can be made from this quickly. He received the Nobel Prize for this in 1918. It is what allows us, even today, to mass grow crops. His work, without hyperbole, feeds billions today.

However, his background in chemistry meant that in 1914, he was asked by his country to contribute to the war effort. After all, that's what one does in war right? He devised heavier-than-air chlorine gas that would go on to be used to kill millions. He resigned from his field in 1939, but the nazis took his research and used it to form Zyklon B - the chemical used in gas chambers on Jews.

He is one of the people whom we ask "does their good outweigh the bad?"