In the sentence “you’re a real trouper”, how should trouper be spelled? I had always thought trouper, but I’m seeing trooper now.
Trouper 1. An actor or other entertainer, typically one with long experience.
State Trooper - a cop
You’re a real trouper. Actors are known for performing no matter what. The show must go on. I think the phrase means you’re determined to complete a job no matter how hard it is.
Bask in your superiority.
Ummm… what about trooper from the same dictionary [bolding mine]? It mentions a slightly different idiom and even says it can be confused with trouper. I’m guessing the idioms just got blended over time. I always thought the OP’s idiom used trooper, as in willing to “soldier on” in the face of hardship.
noun
- a horse-cavalry soldier.
- a mounted police officer; a police officer on horseback.
- state trooper.
- a cavalry horse.
- Chiefly British . a troopship.
**—Idiom - like a trooper, with great energy, enthusiasm, or display: He swears like a trooper. **
Origin:
1630–40; troop + -er1
**—Can be confused: trooper, trouper. **
ABBA spelled it “Super Trouper”, and that’s good enough for me.
Then why do they need understudies?
Ah, if only I could be superior in more than this!!
While carrying on and getting the job done is important to any field, it think it was always ‘‘trouper’’. People seem to be getting sloppier and sloppier.
The Abba song is about a brand of follow-spot, which is itself named after “trouper” as in a member of an acting troupe.
I agree that “trooper” is a more sensible word in this context, as it references military and police troopers, known for their ruggedness, sense of duty, and courage, and not actors, who are known for being narcissistic boobs.
This is for the the same reason you see “there” instead of “their”, “your” instead if “you’re”, and “to” instead of “too”.
I was going to say nobody knows how to spell anymore, but it’s worse than that. Fewer and fewer people seem to even care whether they spell correctly, and nobody outside of the Dope seems interested in correcting them. Sad.
Not knowing your theres from your theirs is sad, but I have yet to see any persuasive evidence that “trooper” is incorrect.
How does one “troup”?
The show must go on, not the actors. 
I also vote for “trouper,” although, in this case, as it is easy to see how the confusion would arise, “trooper” seems to be a much less egregious error than some of the other homophonic malapropisms that one commonly sees.
I learned “trouper,” although “trooper” makes sense to me.
My 1993 Miriam-Webster says trouper is the correct one.