You use the expression ‘To Steal Someone’s Thunder’ to say that someone is making
claims that belong to somebody else.
Example of use: “Don’t resort to plagiarism. All you’re doing is stealing someone’s thunder.”
The origin of the phrase ‘to steal someone’s thunder’ comes from theatre. For centuries, various devices have been used to simulate the loud, rattling noise thunder makes. When, in 1704, literary critic John Dennis invented a new method for producing the sound of thunder but had his play closed by the theatre because of low attendance, W.S. Walsh’s 1893 Literary Curiosities claims he said: “Damn them! They will not let my play run but they steal my thunder.” The theatre in question had used his method of producing thunder during a production of Shakespeare’s Macbeth.