a person who dreams.

a person who lives in a world of fantasy; one who is impractical and unrealistic.

a person whose ideas or projects are considered audacious or highly speculative; visionary.

noun

daydreamer , escapist , fantasizer , idealist , romantic , star-gazer , theorizer , walter mitty , utopian , visionary , castle-builder , enthusiast , fantast , ideologist , john-a-dreams , romanticist