Muk-duk was an anthropomorphic duck.
Muk-duk is the oldest known ancestor of the Clan McDuck (and thereby of Scrooge McDuck). He lived in a large cave and was as fond of fish as his descendant would later be of money. Muk-duk owned all of the world's water (being the first man who'd thought to claim it). In the year 214 200 B.C., he traded it with jealous rival Beegul, ruling it to be worthless, for some more fish. Though theirs was a primitive society, Muk-duk knew how to write with certain ancient hieroglyphics and put down his and Beegul's deal in writing.
Behind the scenes
Muk-duk appears in the 1975 story The Deep Sea Deed.