They are large sexually dimorphic cuckoos that eat fruits and insects and have loud distinctive calls.

The genus Eudynamys was introduced in 1827 by the English naturalists Nicholas Vigors and Thomas Horsfield.

[3][4] A molecular genetic study by Sorenson and Payne (2005) found that the closest relative of Eudynamys is the dwarf koel (Microdynamis parva), and beyond that the thick-billed cuckoo (Pachycoccyx audeberti).

They found that the long-tailed cuckoo (Urodynamis taitensis) of New Zealand and the Pacific, which had earlier been placed in Eudynamys as E. taitensis and sometimes called the long-tailed koel, was more distantly related, along with other members of the tribe Cuculini, including the white-crowned cuckoo (Cacomantis leucolophus), also known as the white-crowned koel.

The evolutionary function is to camouflage her approach to her host's nest and enable her brood parasitism to go undetected.