Warren Bennis was the world's most important thinker on the subject that business leaders care about more than any other: themselves. When he started writing about leadership in the 1950s the subject was a back road. When he died on July 31 st it was an eight-lane highway crowded with superstar professors whizzing along in multi-million-dollar muscle cars.

Mr. Bennis produced about 30 books on leadership. Some of them are classics, such as “On Becoming a Leader” (1989). All are surprisingly readable, stuffed with anecdotes,examples and literary references. He offered advice to leaders from all walks of life.Howard Schultz, the chairman of Starbucks, regarded him as a mentor. Presidents from both sides of the aisle—John Kennedy and Gerald Ford, Lyndon Johnson and Ronald Reagan—sought his advice. If Peter Drucker was the man who invented management (as a book about him claimed), then Warren Bennis was the man who invented leadership as a business idea.

Central to his thinking was a distinction between managers and leaders. Managers are people who like to do things right, he argued. Leaders are people who do the right thing. Managers have their eye on the bottom line. Leaders have their eye on the horizon.Managers help you to get to where you want to go. Leaders tell you what it is you want.He chastised business schools for focusing on the first at the expense of the second.People took MBAS, he said, not because they wanted to be middle managers but because they wanted to be chief executives. He argued that “failing organizations are usually over-managed and under-led”.

Mr. Bennis believed leaders are made, not born. He taught that leadership is a skill—or, rather, a set of skills—that can be learned through hard work. He likened it to a performance. Leaders must inhabit their roles, as actors do. This means more than just learning to see yourself as others see you, though that matters, too. It means self-discovery. “The process of becoming a leader is similar, if not identical, to becoming a fully integrated human being,” he said in 2009. Mr. Bennis knew whereof he spoke: he spent a small fortune on psychoanalysis as a graduate student, dabbled in “channeling”and astrology.

What constitutes good leadership changes over time? Mr. Bennis was convinced that an egalitarian age required a new style. Leaders could no longer crack the whip and expect people to jump through hoops. They needed to be more like mentors and coaches than old-fashioned sergeant-majors. Top-down leadership not only risked alienating employees. It threatened to squander the organization's most important source:knowledge. There is no point in employing knowledge workers if you are not going to allow them to use their knowledge creatively.

The last quarter of the 20 th century often saw Mr. Bennis in despair. He loathed the Masters of the Universe who boasted about how many jobs they had nuked and how much money they had made. “On Becoming a Leader” is full of prophetic warnings about corporate corruption, extravagant executive rewards and short-termism. He also lamented the quality of leadership in Washington, DC.

But he became more optimistic in his last few years, at least about the corporate world. The Enron, WorldCom and Lehman disasters taught businesses the danger of hubris. And a new generation of CEOS, whom he dubbed “the crucible generation” and compared to his own second-world-war generation, were more impressive than their immediate predecessors, characterized not merely by tolerance of other people, but respect for them.

Mr. Bennis's work on leadership was shaped by three different experiences. The first was the Great Depression: in 1932 his father was fired from his job as a shipping clerk without explanation and managed to put food on the table only by helping the mafia transport bootleg alcohol. The next was the Second World War: he led a platoon into battle at the age of 19 and won a Purple Heart and a Bronze Star. The third was more cheerful: the big expansion of American universities during the post-war boom.

The subject of leadership is so popular nowadays that superstar professors made huge money writing about it.

According to Mr. Bennis, firms fail not because of poor management but because of lack of great leaders.

People learn to become leaders by adjusting their own images in other people's eyes just like actors do.

Mr. Bennis' own growth story illustrates the process of becoming a fully integrated human being.

A good leader should first be a very knowledgeable man who can tell people what to do and how to do it.