Definitions of usurper
someone who takes and uses someone or something else's power, right, job, or position without having the right to do so
He is not a legitimate president, he is a usurper.
There are multiple definitions - click on the translation that matches your context.
substantiv
full
noun
someone who takes and uses someone or something else's power, right, job, or position without having the right to do so
He is not a legitimate president, he is a usurper.