The King Eider is a sea duck of the arctic regions of North America. It makes it's living by diving down to the bottom of shallow bays to capture mollusks and crustaceans.
Eider ducks are famous for having particularly soft down feathers on the trunk of their bodies.
Most people were only able to afford products filled with goose down, but the very wealthy could insist on eider down. Because human royalty used to have the custom of wearing brightly colored robes, jewels, etc., when taxonomists encountered a particularly brightly colored species they often gave it a name with a royal reference. Other examples include the Monarch Butterfly and the Queen Parrotfish.