in informal and often derogatory usage, a person who aspires to be someone or something else, i.e. a person who wants to belong to a particular group and who tries to act and/or look accordingly;
e.g. He tried to appeal to them, but they only saw him as a wannabe who wasn't qualified for the position.
(adjective)
aspiring to be a particular type of person, i.e. wanting to be something or someone;
e.g. They are a bunch of wannabe soldiers, always carrying around guns, but none of them have served in the military.