Sir Slye MacDuich was an anthropomorphic duck.
A sneaky medieval member of the Clan McDuck, Sir Slye MacDuich assisted King Malcolm II in 1018 in his conquest of the Angles as a spy. It is joked that this was because even then, it was clear that it would be a MacDuich who'd "know all the Angles". The circumstances of Sir Slye's death are unknown, as is whether he became a ghost haunting Castle McDuck like most of his family.
Behind the scenesEdit
The timeline suggests that Sir Slye MacDuich was the father of Sir Quackly McDuck. This would interestingmy make Sir Quackly the first to call himself McDuck rather than MacDuich.