Leon Black is stepping down as CEO of investment giant Apollo Global Management, following the conclusion of an independent investigation into his interactions with Jeffrey Epstein. Why it matters: Black has long been one of Wall Street's top power brokers, and one of the people responsible for helping to create the modern private equity industry. Backstory: Black has been under pressure for more than a year, due to a personal and philanthropic relationship with Epstein that continued even after the late investment advisor plead guilty to felony prostitution with an underage girl.