Agathyllus () was a Greek elegiac poet from Arcadia, who is quoted by Dionysius of Halicarnassus in reference to the history of Aeneas and the foundation of Rome.
<blockquote>He came into Arcadia, and, in Nesus, married his two daughters Codone and Anthemone. But he himself hastened to the Hesperian land, where he begot Romulus.</blockquote>
Some of his other verses are preserved by Dionysius, although he largely says the accounts of Agathyllus agree with those of another ancient writer, Cephalon.