Ash Carter, the former Defense secretary who oversaw sweeping personnel changes at the Pentagon, including opening all military occupations and positions to women, has died at the age of 68, his family announced Tuesday.  

Carter, who ran the Defense Department from early 2015 to 2017 during President Obama’s second term, died Monday evening in Boston after a sudden heart attack, according to the family’s statement.

While at the Pentagon, the 25th Defense secretary oversaw a range of national security issues, including the launch of the military strategy that would ultimately push back and defeat the Islamic State militant group in Syria and Iraq.  

He also tackled numerous personnel matters, including ending a ban on transgender officers in the military and opening all military positions to women in 2016 — the first time in U.S. history that women could enter certain combat roles previously only open to men.  

Carter “devoted his professional life to the national security of the United States and teaching students about international affairs,” according to his family. “He was a beloved husband, father, mentor, and friend. His sudden loss will be felt by all who knew him.” 

Carter, who was born in Philadelphia in 1954, died just a month after his 68th birthday on Sept. 24. 

“When I think of Ash Carter, I think of a man of extraordinary integrity,” President Biden said in a statement released by the White House on Tuesday. “Honest. Principled. Guided by a strong, steady moral compass and a vision of using his life for public purpose.”

Biden added that Carter “understood the sacred obligation we have to our servicemembers, veterans, and their families.”

Carter attended Yale University, graduating in 1976 with a bachelor’s degree in physics and medieval history, before heading to Oxford University, where he was a Rhodes scholar and received his doctorate in theoretical physics in 1979. 

Carter would remain in academia over the next decade, working at Oxford, Rockefeller University, and M.I.T. before landing various teaching positions and directing roles at Harvard University from 1984 to 1993.  

“He believed that his most profound legacy would be the thousands of students he taught with the hope that they would make the world a better and safer place,” his family said. 

Carter eventually served presidents in both parties over five administrations. He first entered the government service sphere in 1991, when he served as a member of the Defense Science Board, before becoming assistant secretary of Defense for international security policy in 1993 during former President Clinton’s first term.  

While there, Carter was responsible for strategic affairs and overseeing the U.S. nuclear strategy, arsenal and missile defenses. 

The period proved to be a tumultuous one in the world, and Carter found himself heading military planning during what is now known as the 1994 crisis over North Korea’s nuclear weapons program — the result of which was a treaty between the U.S. and North Korea meant to freeze Pyongyang’s nuclear program. 

Carter also served as chairman of NATO’s High Level Group, dealing with new defense and intelligence relationships with former Soviet countries after the Soviet Union collapsed.   

He later served as the Pentagon’s top acquisition official from 2009 to 2011, leading the restructuring of the F-35 fighter jet program, then as deputy Defense secretary from 2011 to 2013, when he oversaw the agency’s massive annual budget and its more than 3 million civilian and military employees.  

He eventually reached the Pentagon’s top civilian role in February 2015 after he was nominated to replace then-Defense Secretary Chuck Hagel and was confirmed 93-5 by the Senate. 

Under Carter, the U.S. military opened all roles to women, including positions in infantry, armor, reconnaissance and some special operations units previously closed to women, and ended a ban on openly serving transgender service members.  

But Carter’s latter move was quickly blunted in 2017 when then-President Trump decided to reimpose the transgender ban, a decision Carter harshly criticized at the time. 

“To choose service members on other grounds than military qualifications is social policy and has no place in our military,” Carter said. 

A Harvard University profile of Carter said he also “led the creation of the military campaign and international coalition to destroy ISIS, designed and executed the strategic pivot to the Asia-Pacific, established a new playbook for the U.S. and NATO to confront Russia’s aggression, and launched a national cyber strategy.”

In addition, Carter was known for his attempt to bring the Pentagon and Silicon Valley together to more quickly bring new technology to the military. While ambitious, the effort had limited success.  

“While he was known for his keen understanding of military technology, nuclear weapons, and international affairs, Secretary Carter loved nothing more than spending time with the troops, making frequent trips to Iraq and Afghanistan to visit U.S forces [with his wife Stephanie],” his family said in its statement. 

Carter on five occasions was awarded the Defense Distinguished Service Medal, the Pentagon’s highest civilian honor. 

After his time in government, he joined Harvard University’s Kennedy School as director of the Belfer Center for Science and International Affairs until his death.

Harvard Kennedy School Dean Douglas Elmendorf, who announced Carter’s death to the school on Tuesday, praised “his lifelong efforts to serve this country, to defend the best values of this country, and to build a safer world for all people.” 

Elmendorf added: “For my part, I want to offer my gratitude for his insight and wisdom, his unwavering commitment to trying to make the world better, his confidence that the Kennedy School can make an important difference in the world, his generous spirit toward his students and colleagues, and his warm and gracious friendship with me. I will miss him so much.” 

Carter is survived by his wife, Stephanie, and children, Ava and Will. 

Updated at 1:42 p.m.