In what year did Mike Godwin introduce Godwin's law? The answer is 1990.
American attorney and author Mike Godwin introduced the idea while participating in early online discussion culture, especially Usenet newsgroups. Godwin described it as an experiment in memetics: he wanted to draw attention to the tendency for long-running arguments to drift toward comparisons with Adolf Hitler or the Nazis. He also argued that careless comparisons could trivialize the Holocaust.
Godwin's law is commonly paraphrased as the claim that, as an online discussion grows longer, the probability of a Nazi or Hitler comparison approaches one. It is an observation about arguments, not a scientific law or a rule that automatically ends a debate. The popular saying that whoever mentions Hitler has “lost” is a later forum convention, not the original principle.
The phrase later spread beyond Usenet to forums, comment sections, social media, speeches, and political writing. Godwin himself has said that a historically informed comparison can sometimes be valid; the problem is reflexive or exaggerated analogy.