Elwyn is the Baudelaire orphans' uncle, mentioned briefly in The Austere Academy.
When Violet Baudelaire was ten and Klaus Baudelaire was eight, the Baudelaire family went to a fair in order to see a pig that Elwyn had entered in a contest. The pig contest turned out to be dull, so the family wandered over to the Biggest Lasagna Contest.
Relation to the Baudelaires
Elwyn is explicitly stated to be the Baudelaire children's uncle, but the exact circumstances of his relationship to them are unknown. He is likely to be the brother of either Beatrice or Bertrand Baudelaire, but it is never stated that he is related to either. As "uncle" is a broadly-used title in the series, and is rarely, if ever, used to refer to a traditional uncle, it also seems likely that Elwyn may not be a brother to a Baudelaire parent at all, and is instead a cousin of some kind, or possibly even a great-uncle. Indeed, it is possible that Elwyn might not be related to the Baudelaires at all, and that "uncle" is a courtesy title that the Baudelaire children gave him out of affection.