By Lily Mae Lazarus
Publication Date: 2026-03-12 11:49:00
Steven Sinofsky isn’t a household name outside tech circles, but he once ran the operating system on more than 90% of the world’s PCs, and now quietly sits as a board partner at one of Silicon Valley’s most powerful venture firms, Andreessen Horowitz. He’s also, as Fortune’s new investigation digs into, a former Microsoft insider who turned to Jeffrey Epstein as a seven‑figure fixer on his way out of the company.
Sinofsky joined Microsoft straight out of grad school in 1989 and climbed from software engineer to president of the Windows division, overseeing Windows 7 and Windows 8. He was once even seen as a possible successor to Steve Ballmer. When he abruptly left in 2012, his departure temporarily knocked billions off Microsoft’s market cap.
Today, he’s a board partner at Andreessen Horowitz, representing the firm on select portfolio company boards and advising founders on product, strategy, and scaling.
What that résumé doesn’t show, however, is…
