Financial terms were not disclosed. William Morris Endeavor said the acquisition will add global reach and depth in sports, fashion and media.
Aside from sports figures including NFL quarterback Peyton Manning, IMG also has clients in the fashion industry. IMG got its start in 1960 with a handshake between Mark McCormack and golfer Arnold Palmer, according to its website.
It has 3,500 employees and operates in more than 30 countries. IMG had been owned since 2004 by private equity firm Forstman Little. William Morris Endeavor was created in 2009 when the entertainment agency William Morris merged with Endeavor, but its roots go back more than a century.
Patrick Whitesell and Ari Emanuel, co-CEOs of William Morris Endeavor, will serve as co-CEOs of the combined company. Emanuel is the brother of Chicago Mayor Rahm Emanuel and is often cited as the inspiration for super-agent Ari Gold on HBO's series "Entourage.