Walter Mitty vs fictitious character

Walter Mitty and fictitious character both are nouns.

Word	Noun	Adjective	Verb	Adverb
Walter Mitty	Yes	No	No	No
fictitious character	Yes	No	No	No

Walter Mitty (noun)	fictitious character (noun)
fictional character created by James Thurber who daydreams about his adventures and triumphs	an imaginary person represented in a work of fiction (play or film or story)