pretender
noun [ C ] uk/prɪˈten.dər/ us/prɪˈten.dɚ/
妄想者，觊觎者
a person who states they have a right to the high position that someone else has, although other people disagree with this
The rebel forces are led by the pretender to the throne (= the person who wants to replace the present king or queen). 叛军由觊觎王位者率领。