Warren Bennis, a business school professor at University of Southern California for 35 years and the author of 30 books on leadership, died last week at the age of 89. The founding chairman of The Leadership Institute at USC's Marshall School of Business, Bennis was known as the "dean of leadership gurus," the Los Angeles Times writes.

His seminal 1989 book On Becoming a Leader, is required reading for any businessperson. Bennis mentored CEOs, trained countless soon-to-be leaders while teaching at Harvard, MIT, and USC, and advised U.S. presidents John F. Kennedy, Lyndon Johnson, Gerald Ford, and Ronald Reagan, The New York Times reports.

Bennis learned his first leadership lessons on the battlefield during World War II as one of the youngest army lieutenants to serve in Europe. Over time he developed inspired leadership theories that disregarded "command-and-control" as a creativity killer and touted passion, integrity, curiosity, and seeing beyond quarterly numbers as a drivers of success. 

Below, check out four leadership lessons from Bennis.

Leaders are made, not born.

In On Becoming a Leader, Bennis wrote that experiencing struggle and hardship molds leaders. The journey to becoming a leader, Bennis wrote, comes as a result of going through a process of self-discovery: "Before people can learn to lead, they must learn something about this strange new world." 

Leadership is like beauty.

Even though he dispensed leadership lessons, Bennis never pretended he knew everything. Pinning down a pearl of wisdom on leadership, he admitted, could be elusive: "To an extent, leadership is like beauty: It's hard to define, but you know it when you see it."

Leading means deeply affecting others

In his 1993 book An Invented Life: Reflections on Leadership and Change, Bennis wrote: "A leader is not simply someone who experiences the personal exhilaration of being in charge. A leader is someone whose actions have the most profound consequences on other people's lives, for better or for worse, sometimes for ever and ever."

A leader is self-aware.

"The leader never lies to himself, especially about himself, knows his flaws as well as his assets, and deals with them directly." 

Curiosity and risk-taking make a leader.

"The leader wonders about everything, wants to learn as much as he can, is willing to take risks, experiment, try new things. He does not worry about failure but embraces errors, knowing he will learn from them." 

A leader sees the big picture.

"The manager has his eye on the bottom line; the leader has his eye on the horizon," Bennis told many audiences, a The Los Angeles Times reported in 1994.

The leader does right.

"The manager does things right; the leader does the right thing," Bennis is also famous for saying.