Walter Mitty

 
Pronunciation: /wɔːltə(r)ˈmɪti/

noun

[often as modifier]
  • a person who fantasizes about a life much more exciting and glamorous than their own: my client is very much a Walter Mitty character

Origin:

the hero of the story The Secret Life of Walter Mitty (by James Thurber, 1939), who indulged in extravagant daydreams of his own triumphs