While watching the 2000 version of Henry James’ The Golden Bowl, I heard the once-common phrase “The deuce only knows…” I’m always looking for vintage profanity, and this appealed to me strongly. I’ve heard it hundreds or thousands of times before, of course, but here it was brought to the fore of my attention. After some brief research, I found ties to 16th Century Northern German, Family Guy, and playing dice. The word deuce seems most strongly tied in meaning to “the devil,” and is used interchangeably in old-fashioned profanity (cf. What the devil and What the deuce).
There are attested uses of the phrase “Was der Daus!” in German from the 16th Century, which has my money for being the real origin of the phrase. Daus meant “devil” though the modern German is “Teufel.” Deuce also means “two” and comes from the French deux. Supposedly, the combination of the German phrase and the playing of dice led to the phrase entering English usage. Rolling two (the Devil’s eyes) inspired the curse, since that was the lowest score and therefore, a loss. I’m not sold on this particular coincidence. It seems too much like folk etymology of the sort you hear in email forwards. Lastly, while I enjoy Family Guy enormously when I hear it, I very seldomly get the opportunity to watch an episode, so the tie to Stewie was lost on me until Google unearthed it.
And when OpenEphyra is given the question What is the origin of the word deuce? the answer is “Watkins.” It offers as evidence this page. That page poses the question What does the word deuce mean? but the answer has nothing to do with my information need. Also, the word Watkins never even appears on that page, so no idea where it came from.