A Harpy has the body of a bird and the face of a hag, droopy breasts, bear-like ears and clawed talons. They also had wings like bats. They are under the rule of Hades who sent them out to fetch the folks who were struggling not to die down to the Underworld. Hades also instructed them to fight Greek heroes.
What is interesting is that in earlier versions of this myth the Harpies were described as beautiful winged maidens. Their demise into the ugly version is thought to be because they were often confused with Sirens.