Kant’s Categorical Imperative is a moral law that states the conditions for when a maxim (a statement of what to do) is morally obligatory. The Imperative takes many formulations but the most common is of ‘Universalisability’ - only do that which you.
"Payback: The Case for Revenge" By Thane Rosenbaum ~ Are vengeance and justice really so very different? No, answers legal scholar and novelist Thane Rosenbaum in Payback: The Case for Revenge—revenge is, in fact, indistinguishable from justice.
I made an infographic, summarizing different ethical theories.