John Morton Blum, a legendary American history professor who inspired thousands of students during his 34-year career at Yale, died Monday morning of complications with pneumonia in North Branford, Conn. He was 90.

Widely regarded as one of the most influential historians of the late 20th century, Blum helped to forge the modern field of American history through his prolific scholarship and writing. In his long tenure at the University, Blum drew hundreds of students to his lectures each year and taught some of Yale’s most famous political alumni. His passion for academics and his dedicated mentorship of students motivated many who passed through his graduate classes to become professors at universities across the country.

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“He of course has a great reputation as a pre-eminent American history scholar,” former Vermont Governor Howard Dean ’71, who took an undergraduate history course with Blum, said in an email Tuesday. “But he could also make history come alive to undergraduate students and he did that for many years. We were incredibly lucky to have him as a teacher.”

Blum came to Yale with a lifelong interest in history and firsthand experience in some of its defining moments.

Born in 1921, Blum grew up in Manhattan and Long Island before attending first Phillips Academy Andover and then Harvard University on scholarship. A year after graduating college in 1943, he travelled to the South Pacific as a member of the United States Navy in World War II. Blum wed his college sweetheart, Pamela Zink Blum, immediately before his deployment, and the marriage lasted for the remainder of his life.

When he returned from the war, Blum continued his history studies and eventually became a professor at the Massachusetts Institute of Technology in 1948. But just nine years later, Blum arrived at Yale as a full professor — joining the ranks of fellow faculty members C. Vann Woodward and Edmund S. Morgan, who were influential historians of the time, and entering campus at a time when the University was experiencing great changes.

As Yale dealt with a tenure crisis in the mid-1960s, struggled to keep the school open during the Vietnam War and worked to incorporate women into the faculty and student body, Blum helped to ease the tensions these issues raised among the faculty, Yale historian Gaddis Smith ’54 GRD ’61 said.

“He was dedicated to the history and to the management of things,” Smith said. “He had a real knowledge of how higher education worked.”

During that time, Blum became the chairman of the History Department and was known among the department’s faculty for his peacemaking abilities, said Morgan, a professor emeritus of history and one of Blum’s closest friends. Morgan added that Blum’s dislike for conflict and his administrative talents led many to believe he would ascend to a deanship or presidency at Yale.

Despite those expectations, Blum remained a professor throughout his time at the University, teaching a number of history courses to both undergraduate and graduate students. Blum’s most famous course ­— History 35 — focused on the populist era, Wilsonian progressivism and New Deal liberalism, and consistently filled all 667 seats in the Law School Auditorium, Blum’s former student William Lilley III GRD ’65 said. The class drew students from every major, Lilley said, adding that Blum was considered an unparalleled lecturer at the University.

“He was the best lecturer I ever heard,” said Laura Kalman GRD ’82, a history professor at the University of California at Santa Barbara who worked with Blum on her dissertation. “He was not a showman, though he could have been. He knew so much and conveyed it so beautifully and with wit when it was appropriate, and students just loved him.”

Sitting among the large crowds that Blum drew were some of Yale’s most distinguished graduates in the 20th century: former President George W. Bush ’68, Senator John Kerry ’66 and Senator Joseph Lieberman ’64 LAW ’67, in addition to Dean.

Kerry, who took History 35 during his time at Yale, said Blum had a significant impact on his students, reminding them of the real connections between people’s lives and political actions.

“Even decades after I sat in his class, I find myself coming back to one lesson in particular that he shared with us,” Kerry said in a Tuesday email. “It’s something I often bring up with my staff and colleagues: that real change only happens in a democracy when people and voters are responding to their ‘felt needs,’ to use the term he taught us.”

In addition to earning recognition as Yale’s pre-eminent lecturer of the time, Blum was also known for his commitment to mentoring students, both academically and personally. Several of Blum’s former students said he helped them develop their writing abilities, and Kalman said he was a “model on how to live.”

Steve Gillon, a former colleague of Blum’s and now resident historian of the History Channel, said Blum taught him at age 27 that “life begins at 30” — encouraging Gillion to find a passion early and spend his life pursuing it.

Despite his well-known academic career, Blum was a private man, who “was intensely fond of his family, friends, and colleagues,” said Pamela Zink Blum, his wife of 65 years.

Blum’s son, Thomas, said his father’s passion and high expectations for society were also evident in his personal life.

“He set a high standard for his children, though tolerant of our faults, and he set a high standard for himself,” Thomas said.

Blum is survived by his wife, three children and three grandchildren. A memorial service will be held in his honor on Nov. 11 at 2 p.m. in Battell Chapel.