I'm trying to imagine who would the richest (fictional) LEAD character, or co-star role in movies. Does not include comic book adaptations (marvel, DC) or movies to include magic and fantasy (lord of the rings, pirates of the Caribbean). Only movies that are closely related to our world in terms of laws of physics, gravity, life longevity, so no flying dragons or people moving objects with their minds.
As a starting point, Ryan Reynolds stars in 6 Underground, and his character is "One". One is a billionaire.
Im going to rule out "The Social Network" which has Mark Zuckerburg portrayed by Jesse Eisenberg, which would kill the discussions plus not really fiction