Peter Drucker(1909-2005): the original and best. He said most of it, really, over seven productive decades. He also said people only called him a guru because they weren't sure how to spell "charlatan".

Russ Ackoff (born 1919): former Wharton professor who rejects much business school orthodoxy with his advocacy of "systems thinking". Worries that managers waste too much time "trying to do the wrong thing righter".