Though I see that through the week, "this week's theme" has been described as "eponyms", on Monday, Anu spelled out a key aspect of these words "This week A.Word.A.Day will feature five people, real and fictional, whose names may appear to be derived from a verb form, but aren't." So I was surprised for a moment to see "tartar" since I didn't think someone would mistake it to mean someone who "tarts". Granted, there are "liar", "beggar", and "scholar", but those are a limited set of cases; the "-ar" ending isn't productive as a "doer" suffix.

On that note, today's "satyr" really surprised me! I can't think of a "doer" word that ends in "yr". (A martyr doesn't "mart" either!)