Former University of Chicago President Robert J. Zimmer led the South Side institution for 15 years as a champion of free speech on campus at a time when the notion was being widely challenged.

“Fundamentally, people are very comfortable with free expression for those that they agree with. And for those that they find disagreeable or wrong, they’re not that eager to have people be able to hear them,” Mr. Zimmer said in 2021. “The whole point of education is focused around ongoing intellectual challenge and open discourse.”

Under his leadership, students were put on notice in 2016 that the university did not support canceling speakers because their topics might prove controversial or condone intellectual “safe spaces” where students could retreat from ideas at odds with their own.

The ideals were tested in 2018 when a university business professor invited Steve Bannon, who served as an adviser to former President Donald Trump, to the campus to debate globalization and immigration. The university backed the professor amid protests, although Bannon ultimately backed out of the debate.

Several years earlier, in 2014, Mr. Zimmer appointed the Committee on Freedom of Expression, which declared a commitment to free expression that became known as the “Chicago Principles.”

They’ve been adopted by more than 80 colleges and universities around the country, according to a news release from the university. 

Mr. Zimmer died Tuesday at home in Chicago after a battle with brain cancer. He was 75.

He served as the university’s 13th president from 2006 to 2021, when he transitioned to the role of chancellor after surgery to remove a malignant brain tumor. He became chancellor emeritus on July 1, 2022.

Mr. Zimmer was a pioneering mathematician who spent nearly four decades at the university as a faculty member and administrator.

He led the expansion of financial support for students, established the university’s first engineering program and expanded the university’s global presence through new centers in Beijing, Delhi and Hong Kong.

“He had no patience for bureaucracy nor wasting time,” said Joseph Neubauer, former chair of the Board of Trustees. “Bob cultivated a mission-driven sense of urgency in his staff, about ten of whom were recruited to lead institutions in higher education.”

More than a half-dozen former administrators and deans who served under Mr. Zimmer have been appointed to lead universities and colleges such as Caltech, Dartmouth, Northwestern and Vanderbilt, according to the university.

Before taking the reins at University of Chicago, Mr. Zimmer served as provost of Brown University.

He grew up in New York City’s Greenwich Village, a diverse place during the 1950s and ‘60s that made him feel “tolerance in a deep way.”

Mr. Zimmer is survived by his wife, Shadi Bartsch-Zimmer, a faculty member at the University of Chicago, and his sons Alex, Benjamin and David, from his previous marriage to Terese Schwartzman.

Services are being planned.