I've tried looking into this, but mostly I just get "factual" I'm looking for the opposite of a person who is a legend for doing good things. What would the opposite of Odysseus be? Kind of like for famous there's infamous. What's a person who's a legend, but not for good reasons? Is there a word for it?
We can say
He was a notorious criminal.
Governor X was a politician of great disrepute in the 1930s.
Rather too many questions here. Legend or myth, as a kind of account of events, is often opposed to history, which in this context is sometimes modified with sober. As for a person’s being a legend, the opposite would be a nobody or someone whose name is deservedly forgotten; thus, we cannot name an opposite to Odysseus in the sense of one who is as lacking in immortal fame as Odysseus is endowed with it. (In some other senses, we can indeed name opposites to him: his opposite in terms of his fondness for deception, for instance, is Achilles.) One who is known to fame for a bad thing or quality rather than a good one can be said to be a by-word for it (or byword: M-W “someone or something that is closely connected with a particular quality”), as Timon for misanthropy, Thersites for obstreperous rudeness, Helen for calamity. Of course, one can be a by-word for a good thing, too, as Helen for beauty, and—depending on your point of view—Croesus for wealth.