1981, originally American English surfer slang, from casual pronunciation of want to be; popularized c.1984 in reference to female fans of pop singer Madonna.
Someone who aspires to be someone else, esp a star or hero: Rambo Wanna-be's/ A ''poser'' or a ''wanta be'' is someone who tries to be like someone else
[1980s+ California surfers & black street gangs; fr imprecise or dialectal pronunciation of ''want to be'']