I believe all billionaires have done something good. I don't think that makes them good people due to the staggering amount of wealth they withhold from the population.
Doing good things, doesn't make you a good person. Donating millions is nothing when you have billions.
If I had to choose a specific, I'd say Bill Gates. I've never fact checked it but I've heard he set up multiple charities and donates for helping children, seems like a great thing to do.