The Filet-O-Fish received the fictional McDonaldland character Captain Crook in the 1970s.
Captain Crook was designed as a pirate-themed character associated with the fish sandwich. His costume, speech, and nautical imagery reinforced the connection between the character and the Filet-O-Fish without requiring the advertisement to explain the menu item at length.
McDonaldland used this kind of character branding to give individual products or product ideas a memorable identity. Captain Crook is therefore different from the Hamburglar, whose advertising role centered on stealing hamburgers, and from Grimace, whose early identity was connected with milkshakes.
The character is now less prominent than many other McDonald’s mascots, which can make the association easy to forget. In the 1970s, however, Captain Crook was part of the brand’s broader fictional advertising world.