Origins: Stealing someone's thunder

The above phrase, meaning to take someone else’s glory or credit, originated from an expression of the London playwright John Dennis (1657-1734), who is no longer remembered for his plays but who lives on in the phrase. Dennis invented a new method of simulating the sound of thunder as a theatrical sound effect and used it in his unsuccessful play Appius and Virginia. Although his technique is not now known, until then thunder had been simulated by rolling metal balls in a wooden bowl. Shortly after his play came to the end of its disappointingly short run he heard the same thunder effects used at a performance of Shakespeare’s Macbeth. Dennis was understandably furious. ‘Damn them!’, he fumed, ‘they will not let my play run, but they steal my thunder!’ The phrase thereafter gained wider circulation for taking the credit belonging to someone else.

Source: http://www.phrases.org.uk/meanings/steal-ones-thunder.html