Leonard Anthony Leo (born November 1965) is an American lawyer, businessman, and conservative legal activist. He is the chairman of CRC Advisors and is renowned for his influential role in shaping the federal judiciary through the Federalist Society, where he serves as co-chairman of the board of directors alongside Steven Calabresi. Previously the longtime executive vice president of the organization, Leo has been a key architect of conservative judicial appointments, particularly as a pivotal advisor to President Donald Trump on nominations, vetting and promoting conservative judges including several Supreme Court justices. He has managed billions in funding for conservative causes through affiliated nonprofits, notably the Marble Freedom Trust, which received a $1.6 billion donation from Barre Seid, establishing him as a central figure in conservative 'dark money' networks. A key node in his judicial influence network is the Judicial Education Project (operating as The 85 Fund), for which DonorsTrust facilitates 99% of the funding.

Deeply influenced by his Italian immigrant grandfather, a tailor who rose to vice president at Brooks Brothers, Leo credits this background for his views on America. A devout Catholic with alleged ties to Opus Dei-style Catholicism, he attended Cornell University (BA 1987) and Cornell Law School (JD 1989), interned for Senator Orrin Hatch, and clerked for a federal judge early in his career. His leadership extends to organizations such as the Catholic Association (board member), and previously the U.S. Commission on International Religious Freedom. Leo maintains close personal friendships with Justice Clarence Thomas and has met privately with major donors like Barre Seid and Diana Davis Spencer.

He has faced criticism for opaque funding practices and personal ties to the judiciary; notably, 2023 reporting revealed he arranged tens of thousands in consulting payments around 2011-2012 to Ginni Thomas, wife of Justice Clarence Thomas, via a group he led, with her name omitted from billing paperwork (ProPublica/Washington Post). Controversies include allegations of steering billions in anonymous donations to influence elections and courts, with critics labeling him a 'moneybags kid,' though no criminal charges have been filed and his networks face ongoing investigations into ethics and tax-exempt compliance.