I often heard this saying used when referring to members of the theatrical industry, “He’s a real trooper!”  As my maternal grandmother appeared on stage in London vaudeville times, I believed that the saying should be, “He’s a real trouper!”

Which is correct?

To many English speakers, a trooper is a policeman or soldier. In the U.S., many state police forces refer to their members as troopers.

A trouper is the member of an acting group called a troupe.

The words troop and troupe both entered English from the same French word:

Troop: 1540s,”body of soldiers,” from the French troupe.

Troupe: 1825, “company, band or ensemble,” from the French troupe.

The Oxford English Dictionary gives these definitions of the colloquial uses:

Trooper: A brave or stalwart person.

Trouper: A reliable, uncomplaining person; a staunch supporter or colleague.

Therefore, if the context has to do with courage, trooper is appropriate. If the context has to do with cooperation, dependability, acting and the show business attitude of “the show must go on,” then trouper is the correct word to use.