Using someone else's achievements and/or good name for personal benefit. Posing as someone with status and placing those achievements on yourself.
Aaron Clinton Atkins III would have you believe he is as talented as his uncle Juan, however he is an impostor.
Someone who pretends to be someone else, usually in a serious setting, where the impostor is doing some sort of damage
That surgeon who did Jane's tonsilectomy? Turns out, he was an impostor. He had a real job as an orderly in the hospital, but he was really good at snowing people and hacking computer records. They've got him locked up and his two wives are trying to bail him out.