While I'm not one to fawn after billionaires, I found his life story and personality really fascinating. He really seemed to maintain a humble approach, and in the Numberphile interview, which is excellent, he really emphasized the notion of luck in success. He donated a ton of money in very targeted ways that have been extremely successful. I think because of his humble approach, lack of self-promotion, etc., he's a bit unknown outside certain circles, but his impact in certain areas has been big.

While I wish that our country didn't have to rely on billionaires spearheading initiatives, which often goes the wrong way, Simons was absolutely an example of one of the good ones.

https://www.youtube.com/watch?v=QNznD9hMEh0