The Knobbed Hornbill, Aceros cassidix, also known as Sulawesi Wrinkled Hornbill is a large black hornbill with a yellow bill, white tail feathers, pale blue skin around eye, blackish feet and bare dark blue throat. The male has rufous buff face and neck, orange-red eyes and a high reddish casque on top of bill. The female has black face and neck, yellow casque and brownish eyes.

An Indonesian endemic, the Knobbed Hornbill is distributed in the tropical evergreen forests of Sulawesi, Buton, Lembeh, Togian and Muna Island.

As with other hornbills, the Knobbed Hornbill is believed to be a monogamous species. The diet consists mainly of fruits and figs. The female sealed itself inside a tree hole for egg-laying. During this time, the male will provide foods for the female and the young.

The Knobbed Hornbill is the faunal symbol of South Sulawesi province.

Widespread and common throughout its native range, the Knobbed Hornbill is evaluated as Least Concern on the IUCN Red List of Threatened Species.