Friend of Dorothy outside bank's enigmatic millionaire (6)

I believe the answer is:

gatsby

I'm a little stuck... Click here to teach me more about this clue!

'millionaire' is the definition.
(I have seen 'Novel millionaire' mean 'gatsby' so perhaps 'millionaire' could also mean 'gatsby')

I can't explain the rest of the clue.

Can you help me to learn more?

(Other definitions for gatsby that I've seen before include "Classic novel by F Scott Fitzgerald - 'The Great . . . . . .'" , "F Scott Fitzgerald wrote 'The Great . . .'" , "great fictional character" , "Scott Fitzgerald hero" , "Fitzgerald's tycoon" .)

I've seen this clue in The Independent.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.