Well if you believe in religion then God has the most blood on his hands. Considering he flooded the earth killing everyone except Noah and 2 of every animal.
If your talking humans then yeah probably the guy who dropped the atom bombs on Nagasaki/Hiroshima.
But If you mean actual physically killing with a handheld weapon then I guess Christman Gniperdoliga. He is responsible for almost 1,000 murders in the 16th century.







