Whoever has the power to repay good with good, evil with evil, and also actually repays, thus being grateful and vengeful, is called good; whoever is powerless and unable to repay is considered bad.
Nietzsche argues that ‘bad’ originates as an aristocratic designation for the powerless and impotent, entirely distinct from the moralized concept of ‘evil’ generated by ressentiment.
, On the Genealogy of Morals, 1887thesis