https://www.youtube.com/watch?v=GF2qlhcc55U Not much is known about the extent of the charity work but he clearly does his bit. There are videos (such as the one above) which show 'Taker promoting certain charitable organisations. Undertaker is a private guy who isn't active on social media and doesn't go around bragging about how much he does (the way WWE do with John Cena). But once he steps away from the ring for good it could be something that he focuses more energy on. Having The Undertaker representing a charity will instantly give it more visibility. He could use his celebrity to do some really good things.