The actual answer: hedge fund manager Bill Ackman. https://www.institutionalinvestor.com/article/2bswuu1nfc040h... & https://finance.yahoo.com/news/visa-suspends-payments-for-ad...

> But he was friendly with Mastercard’s then-CEO Ajay Banga, whom he had met through a mutual friend. Ackman texted Banga, providing a link to Kristof’s story with his tweet: “Amex, VISA and MasterCard should immediately withhold payments or withdraw until this is fixed. PayPal has already done so.” (Ackman was unaware that American Express already did not allow its card to be used on adult sites.)

> Banga quickly wrote back: “We’re on it.”

> Then things began to move. Within days, Mastercard announced it had “instructed the financial institutions that connect the site to our network to terminate acceptance” of [PH] charges, saying it had found evidence of illegal activity and was continuing to investigate.

EDIT: The antisemitism in some replies is disgusting and I reject it entirely. This post is about a specific, publicly reported action by one individual, not about any religious or ethnic group. Any attempt to turn this into conspiracy-mongering is bigotry, not analysis. I don’t want that associated with my comment.