Rather a significant number of characters in that series that based on real people, to the point that many characters use the real person's actual name. The cast section of the Wikipedia page shows the extent:
https://en.wikipedia.org/wiki/Boardwalk_Empire#Cast_and_char...
The references beyond that are quite interesting as well. I always felt that the character Nelson Van Alden (also George Mueller) was a reference to Baby Face Nelson, who was known also as George Nelson.