BALTIMORE — Late one night in the fall of 2020, when Kizzmekia Corbett learned the vaccine she had helped design was highly effective against the coronavirus, there was only one person she wanted to call: Freeman A. Hrabowski III, the longtime president of the University of Maryland, Baltimore County.

At 34, Dr. Corbett was the first Black woman to achieve such a feat, a groundbreaking development in the fight against the deadliest pandemic in recent U.S. history. But all she could think about was the man she had met as an 18-year-old freshman at the university, who immediately recognized her thick Southern accent and her potential to make history.

“I had to call someone who understood all that I had been through — what it meant to even get a Ph.D., what it meant to traverse this space,” said Dr. Corbett, now an assistant professor of immunology and infectious diseases at Harvard’s T.H. Chan School of Public Health. “So I called Freeman.”

Dr. Hrabowski, who retired last week after leading U.M.B.C. for 30 years, is renowned in academic circles for transforming what was once a regional commuter school into the country’s strongest pipeline of Black graduates in science, technology, engineering and related fields.

The school’s Meyerhoff Scholars Program, whose alumni include Dr. Corbett, has served as a barrier-breaking model for colleges nationwide. The University of North Carolina at Chapel Hill and the University of California, Berkeley, are among those that have replicated it.

As the nation’s top producer of Black undergraduates who go on to complete a Ph.D. in the natural sciences or engineering, U.M.B.C. has cracked one of the most vexing conundrums in higher education — the lack of Black students excelling in the sciences.

For these achievements, Dr. Hrabowski acquired something like celebrity status over the course of his tenure. He has written four books, given thousands of speeches, made it onto influencer lists and seen hundreds of graduates go on to obtain professorships and other positions at some of the country’s most prestigious institutions.

But Dr. Corbett’s call that night was also a testament to a lesser-known but arguably as important part of Dr. Hrabowski’s legacy: serving as a mentor to a cross-section of leaders in science and academia, many of whom have come to emulate his style as much as his substance.

When the Howard Hughes Medical Institute recently announced a $1.5 billion program to support the next generation of diverse faculty in science, technology, engineering and math, it named the initiative the “Freeman Hrabowski Scholars Program” to make the mission clear, said Leslie Vosshall, its vice president and chief scientific officer. “If every institution took his recipe,” she said of Dr. Hrabowski, “didn’t change any ingredients, didn’t cut corners, that would transform STEM education in the United States.”

College and university presidents across the country point to “Freeman lessons” that are modeled in classrooms and boardrooms every day.

James P. Clements, president of Clemson University and an alumnus of U.M.B.C., recalled how Dr. Hrabowski had coached him for the interview that led to his first presidency, at West Virginia University. “I wouldn’t be a college president if it weren’t for Freeman,” he said, “and 14 years later, he’s still coaching me.”

Paula A. Johnson, the president of Wellesley College, met Dr. Hrabowski years ago as a young faculty member at Harvard, when he was receiving an honorary degree and she was assigned to act as his host. He had specifically asked for a professor of color.

“He is always thinking about his role, not just in terms of the honor he’s getting, but who else he can include and advance. He is continuously paying it forward, in big and small ways,” she said.

Starting this week, Dr. Hrabowski, 71, will continue that work in a number of advising positions, including as the inaugural centennial fellow at the American Council on Education, which represents 1,700 colleges and universities.

“There are many ways to think about influence, and some of them are more glittery than others,” said Ted Mitchell, president of the council. “Freeman has actually reached into all of our hearts and asked us to remember what education is for. He has been the moral compass for all of us, and that makes him the most influential leader of higher education in our generation.”

Born in Birmingham, Ala., Dr. Hrabowski came of age in the thick of the Jim Crow era. The notion that Black children didn’t deserve a quality education brought out the fighter in the self-described “fat, nerdy kid who could only attack a math problem” at a very young age.

He was 12 when he participated in the historic Children’s March inspired by the Rev. Dr. Martin Luther King. He was among the hundreds of boys and girls arrested while they marched for equal rights, and spent five days in jail.

Dr. Hrabowski has largely declined to discuss the details of what he saw and experienced in the Birmingham jail. Some of it will forever remain unspeakable, he said. But in an interview, he recalled a visit from Dr. King.

“What you do this day will have an impact on children not yet born,” Dr. Hrabowski remembered him telling the jailed children.

Dr. Hrabowski credits his perseverance to his upbringing in 1960s Birmingham — from the small but vibrant middle-class neighborhoods that molded him and other Black leaders, including Angela Davis and Condoleezza Rice, to his church, where funerals were held for three of the four Black girls who died after a white supremacist terrorist attack.

“Our parents and teachers and ministers insisted that we not define ourselves as victims — in spite of the overt racism all around us,” he said. “Rather, we were taught to believe in ourselves and to strive to be twice as good, because we knew the world was not fair.”

He went on to attend Hampton Institute, a historically Black college, earning a degree in mathematics at 19. In graduate school at the University of Illinois at Urbana-Champaign, Dr. Hrabowski said, he learned “how lonely a student of color can be in a classroom.”

He received a master’s degree in mathematics and a Ph.D. in higher education administration and statistics there, and began his career in higher education administration. Later, he moved to Coppin State University, a small, historically Black school in Baltimore, where his reputation as a change agent who championed students, even at the expense of offending adults, put him on U.M.B.C’s radar.

It was a young institution, the first campus in Maryland to accept all races, craving leadership that matched its ambitions.

When Dr. Hrabowski arrived at U.M.B.C. in 1987 as vice provost, one of the first questions he asked was why an aspiring research university was graduating only double-digit numbers of Black students with science degrees. It was 20 years after integration, and the average Black G.P.A. was barely 2.0, compared with 2.50 for white students; there was at least a 20-point gap between the graduation rates for the two races.

The following year, he convinced the Maryland philanthropist Robert Meyerhoff to financially back his quest to prove that with the right guidance and resources, Black students could excel in science in large numbers at a predominantly white university.

“It had not been done before in the nation,” Dr. Hrabowski said. “People did not think it was possible, because they had not seen it.”

The two co-founded the Meyerhoff program, which has since graduated more than 1,400 students, most of them African Americans, in science and engineering. Its graduates, who receive financial scholarships, academic guidance, research experience and mentoring, fan across the nation to the most prestigious doctoral programs and prominent research spaces.

There is no longer a graduation gap between Black and white students at U.MB.C., but Dr. Hrabowski doesn’t want to be remembered only as the “guy who produced Blacks in science.” He is equally proud that the school produced the first Black speaker of the Maryland House of Delegates, who was also the first woman to hold that position.

From the time he became president in 1992, his goal was to create and model a culture of “inclusive excellence” — in which all students are supported in the ways they need to succeed.

The U.M.B.C. campus has grown to 675 acres to incorporate $1.2 billion worth of construction, a separate research park with more than 120 biotech labs and cybersecurity companies. But on a recent day, it wasn’t the glitzy new buildings that Dr. Hrabowski gushed over. It was the campus’s main thoroughfare, Academic Row, where more than 100 flags represent the nations of origin of the school’s roughly 14,000 students.

“It’s hard for a Black president to say, ‘I care about all races’ and be heard,” he said.

But he was.

Kaitlyn Sadtler followed her sister there from a rural suburb in Maryland. She had never thought about becoming a Ph.D.; she was just grateful to get into an affordable state college. But she now has advanced degrees from Johns Hopkins University and M.I.T. Dr. Sadtler is leading a 10,000-participant N.I.H. study on Covid-19 antibodies at the National Institutes of Health, where Dr. Corbett helped design what became the Moderna vaccine.

But reflecting on her time at U.M.B.C., Ms. Sadtler, pointed to memories that had little to do with science: her half-Japanese roommate who coaxed her into eating rice, which she had vowed to never eat again after being raised on Minute Rice; and the beloved Black president who knew every student’s name and major.

“I come from a very white area, so I like to say U.M.B.C. started my education on multiple levels,” she said. “I was getting exposed to new things, but I didn’t ever feel uncomfortable or out of place.”

Twenty-six years into Dr. Hrabowski’s efforts to build an inclusive community, he got a painful reality check.

In 2018, the school faced a class-action lawsuit accusing it of violating Title IX, the federal law that prevents sex discrimination, by working with county law enforcement officials to cover up reported sexual assaults. The lawsuit roiled the campus, spurring student protests and drawing furor from alumni.

Dr. Hrabowski was invited to a meeting on campus that September, with an unusual request: Do not speak.

Instead, he was asked to listen as female students discussed their history with sexual harassment. The lawsuit was dismissed in 2020, but the issues it brought to light remained a subject of intense scrutiny and led to changes at the university.

“It was a very dark moment,” Dr. Hrabowski said. “We may have been in compliance with the law, but it became clear that we needed to do much, much more.”

He has drawn on the few fraught episodes of his tenure to help guide other presidents navigate their own challenges.

David A. Thomas, president of Morehouse College, turned to Dr. Hrabowski a few years ago, when he was starting an online degree program at the university. It spurred contentious debate among faculty who were concerned it could diminish the Morehouse brand.

He took an initial vote on the measure, and it passed by a small margin. Dr. Hrabowski told him to “keep the debate going,” Dr. Thomas recalled. The final vote was more than 70 percent in support.

“Without consultation with Freeman, I would have taken that first vote with a bunch of abstentions and said we got a positive result,” Dr. Thomas said. “But I think we benefited by continuing the conversation. That was a ‘Freeman lesson’.”

Dr. Hrabowski’s successor is Valerie Sheares Ashby, a chemist and the former dean of Duke University’s Trinity College of Arts and Sciences. She became U.M.B.C.’s first female president on Aug. 1.

Years ago, Dr. Sheares Ashby got a solid vote of confidence from Dr. Hrabowski, who would become one of her most trusted mentors, before she had even led a department. At the end of their first meeting, he turned to the young faculty member and said: “You’re going to be a president — a great president — someday.”