A legend in the making.
An individual who is on the verge of a legendary status.
Showing appreciation to someone due to a favour.
Note: The word 'Legend' is often over used for individuals who are truly not worthy of the title. Using the word 'Ledge' can be a more meaningfull fit, without taking anything away from the person.
Billy: Tom really helped me with my assignment man, he is a Ledge!
Sam: 'Joe can you cover my shift on saturday? I really need it off.'
Joe: 'ummm... OK'
Sam: 'Aw cheers mate, your a Ledge!'