I was a junior person working at Interplay in 1989 when The Duck was introduced into a game.
The story in this thread is true except for a couple of details. This would have been 1989. Todd Camasta (who had indeed been the lead artist for Battle Chess) put in the duck, but it was a still image, not animated, and it was in the NES game “Total Recall”. The duck was standing there on a Mars-scape screen – it may have been the game’s final screen – and supposedly the approver did indeed look at it and say “Looks great – just get rid of the duck.” The duck served its purpose.
Scott Bieser, another longtime Interplay artist who also worked on the game, thinks the idea came from Troy Worrell (VP of development at the time) or from Mike Quarles (a programmer on the project).