As you’d know, the phrase "stealing your thunder" is used when someone else appropriates your ideas for their own benefit, undermining your credit.
The phrase interestingly has its roots in theatre.
The story is that seventeenth century British dramatist John Dennis used a new method of creating the sound of thunder for his production Appius and Virginia (1709). It isn’t clear from the texts available today what this method was, some sources say it was rattling a tin sheet on the backstage, others say it was rolling metal balls in bowls of wood.
Whatever it was, the play Appius and Virginia flopped and Drury Lane Theatre, London, which was running the play, stopped further shows of it. Playwright John Dennis was miffed – he had a high opinion of his work.
Soon afterwards he went to Drury Lane Theatre for the performance of Shakespeare’s Macbeth. He found them using his own new method of creating thunder.
Enraged, John Dennis exclaimed:
That is my thunder, by God;
the villains will play my thunder, but not my play.
The exact words are in doubt, some sources say he said:
Damn them! They will not let my play run,
but they steal my thunder.
Or words to that effect. And so the idiom "stealing one’s thunder" was born.