Warren Bennis, who died last summer, was one of the world’s most influential thinkers on the topic of leadership. In dozens of books and articles, he identified the qualities that make a brilliant leader and showed how to attain them. As HBR’s editor in chief, Adi Ignatius, notes in the May 2015 issue of HBR, “No one wrote better, or with more clarity, about the imperative and challenges of being a great executive.”