Minthe is one of the Naiads of the river Cocytus. It is the river of wailing. She and Hades had an affair before Persephone did, and they had a secret affair when Persephone married him. There have been many stories saying that maybe Persephone cursed her and turned her into a mint plant, but nothing is certain, because Persephone is usually seen as a caring goddess, quite unlikely of her to do it.
Even though she might have been cursed as a mint plant, she still has a very high spirit.
Minthe's official Greek name is Μινθη.