I'm not sure of the origin of the idiom, though I believe it to mean a single-function or single-use person, animal, or object. It's often used after a lackluster or anticlimactic event in my experience. Perhaps the origin lies in rodeos of the American west or carnival shows? Merriam Webster online corroborates my definition. https://www.merriam-webster.com/dictionary/one-trick%20pony Also according to Merriam Webster, its first known use was in 1980.

From the Merriam-Webster dictionary: one-trick pony (noun) Definition of one-trick pony : one that is skilled in only one area also : one that has success only once First known use with this meaning: 1980 Example: The camera isn't very impressive next to those in some smartphones, and $250 is a steep price for a one-trick pony.

Hi Dawid, it does not just have to be a person in reference, it can also be used to describe other nouns. We refer to someone or something as a "one trick pony" with only one apparent special feature, talent, or area of expertise.

We often use it to refer to a persons' limited talents or the fact that they always have the same reaction to situations. You could refer to comedian Jim Carey for example as a 'one trick pony'.