Harvard University announced its largest single gift ever Wednesday, a $400 million donation from alumnus and hedge-fund billionaire John A. Paulson to the School of Engineering and Applied Sciences.

The university is in the midst of an effort to raise $6.5 billion by 2018. Its endowment was the largest in the country according to a national ranking last year, at about $36 billion. Last year, Harvard was given a $350 million gift from the family of T.H. Chan for its school of public health.

The gift is not the largest ever to higher education, but it is certainly among the biggest. (The highest, at least according to an inflation-adjusted ranking by Indiana University’s Lilly Family School of Philanthropy of public gifts by U.S. donors since the year 2000, was a 2001 donation to Stanford University, from the William and Flora Hewlett Foundation, which would be the equivalent of $532 million in 2014.)

The school, whose labs have recently developed wonders such as an implantable cancer vaccine and a robot that can build itself from a flat sheet, will be named in Paulson’s honor.

“SEAS is the next frontier for Harvard,” Paulson said in a statement, “and its expanding campus in Allston promises to become the next major center of innovation.”

Paulson graduated from the business school in 1980 and founded Paulson & Co. with a single employee in 1994. The firm specializes in alternative investments — some of which have been wildly successful, some of which have faltered — and now manages more than $19 billion with more than 125 employees.

He’s now the 113th richest person in the world, according to the Bloomberg Billionaires Index, with $11.3 billion to his name. Paulson has donated to the arts, conservation, health care and education causes over the years, and served on numerous nonprofit boards.

Not everyone was impressed, some because of Harvard’s substantial endowment, others because of the way Paulson became so wealthy, in part, by betting against the overinflated housing market nearly a decade ago. On social media, one commenter turned up his nose at money “made betting your kids would be homeless.”

A small investment team noted bitterly that Harvard’s endowment is larger than the gross domestic product of roughly half of all countries, with returns greater than 15 percent last year, and speculated, “the same sum he donated to Harvard could have fed nearly 240,000 hungry elementary school students for an entire year, or roughly the entire under-18 population of Washington, DC for 2 years.”

Others were delighted.

“There is no easy formula for innovation, in both the physical and digital worlds — in both atoms and bits — but SEAS accomplishes both,” Michael D. Smith, Edgerley Family Dean of the Faculty of Arts and Sciences  said in a statement, citing examples such as the “sharing economy’ entrepreneurship of Airbnb founder. “SEAS demonstrates what’s possible when you combine a world-class research and teaching environment with a fundamental commitment to the liberal arts. That’s engineering at Harvard. That’s what this gift will multiply.”