Jk Rowling. She was (I think) the only billionaire to ever debillonaire themselves without dying (i.e., she donated so much wealth to charity that she was no longer a billionaire).
But then she decided to dedicate herself to making trans people's lives miserable...
Good question, I never actually looked into it. According to her Wikipedia page:
She established the Volant Charitable Trust in 2000, and co-founded the charity Lumos in 2005. Rowling's philanthropy centres on medical causes and supporting at-risk women and children. In 2025, Forbes estimated that Rowling's charitable giving exceeded US$200 million. She has also donated to Britain's Labour Party, and opposed Scottish independence and Brexit.