On a Thursday in February, the same morning that he was scheduled to meet with the widow of Alexey Navalny, Joe Biden found himself at the Fairmont Hotel, atop Nob Hill, staring at a total stranger half his age. Dustin Moskovitz, the 39-year-old billionaire seated across from him, was probably more responsible than any other donor for vaulting Biden into the presidency. And yet, somehow, the two had never met.

Moskovitz, like the other Harvard kids who won the roommate lottery with Mark Zuckerberg and became Silicon Valley royalty, is often dismissed as some accidental co-founder of Facebook, the ultimate example of being in the right place at the right time. But Moskovitz caught lightning in a bottle a second time with Asana, the public software company he founded in 2008. He and his partner in all things, former Wall Street Journal reporter Cari Tuna, whom he met on a blind date, would become the patron saints of effective altruism—particularly during the post-S.B.F. correction—with $25 billion to dole out through their Open Philanthropy charity.