ㄇㄠˋㄇㄧㄥˊㄉㄧㄥˇㄊㄧˋmàomíng‑dǐngtì

冒名顶替
  1. 假冒他人名義取代他人身分行事 應考冒名頂替失去考試資格」。

to assume sb's name and take his place (idiom)​; to impersonate, to pose under a false name