Oliver Williamson died yesterday at age 87, I do not know of what. He was famous as the main developer of New Institutional Economics, following the influence of Ronald Coase, which emphasizes the role of transactions costs in the formation and development of economic (and some other) institutions. He received the Nobel Prize in 2009, along with Elinor Ostrom, but his influence was really quite vast for a man from a working class background, born in Superior, Wisconsin.
I checked, and although there may be another one ahead of him, as near as I can tell at his death only one other living economist had more Google Scholar citations. Andrei Shleifer has about 295,000 (h has a problem getting that trip to Stockholm because of his infamous corruption problem involving Russia), while Ollie had about 276,000. The all time leader is Karl Marx at about 333,000.
A reason for this is that his work became enormously influential across other disciplines, especially management and law. Indeed, he is one of the few individuals I know of (I know of only one other, Shyam Sunder at Yale) who was simultaneously in an economics department, a separate business school (I think the Management dept), and a law school, all of which he was at UC-Berkeley. The only other person I know of who was in more departments was the late polymathic Nobel Prize winner, Herbert Simon, more on him below.