In Greek mythology, Mestra was the shape-changing daughter of Erysichthon of Thessaly. After Demeter cursed her father with insatiable hunger, he sold her repeatedly; Poseidon (who had loved her) gave her the power to transform and escape each buyer. Ovid also makes her wife of Autolycus. Antoninus Liberalis calls her Hypermestra. Distinct from Danaid Mnestra and from other Mestrai.
Adapted from Wikipedia, "Mestra" · CC BY-SA 4.0
I.Hunger and metamorphosis
Erysichthon violated Demeter's grove and was cursed with endless hunger. Having spent his wealth on food, he sold Mestra into slavery. She prayed to Poseidon, who transformed her into a fisherman; the buyer left deceived. Discovering her gift, Erysichthon sold her again and again as animals of every kind; she always escaped and returned with the purchase price until, in Ovid, he finally ate himself.
In Hesiod's Catalogue of Women the sales are framed as bride-prices to suitors (including Sisyphus seeking her for Glaucus). Poseidon carries her to Cos, where she bears Eurypylus.
II.Marriage and names
Ovid names Autolycus as her husband. Antoninus Liberalis' parallel uses Hypermestra / Aethon for daughter and father. Atlas id mestra-thessaly is Erysichthon's daughter — not the Danaid listed as Mnestra in Apollodorus.