Ash Carter, who served as Secretary of Defense in the final two years of the Obama administration, died at the age of 68.
Carter, who joined the Defense Department during former President Bill Clinton's administration, is remembered for opening military combat jobs to women and ending a ban on transgender people serving in the military.
Carter died after suffering a heart attack on Monday evening, according a statement Tuesday from Douglas Elmendorf, dean of Harvard University's Kennedy School. Carter had served as as director of the school's Belfer Center for Science and International Affairs.
In December 2015, after three years of study and debate, Carter ordered the military to open all jobs to women, removing the final barriers that kept women from serving in combat, including the most dangerous and grueling commando posts.
The following year, Carter, a native of Philadelphia, was responsible for ending the ban on transgender troops serving in the U.S. military, saying it was the right thing to do.
"Americans who want to serve and can meet our standards should be afforded the opportunity to compete to do so," Carter said in June 2016, laying out a one-year plan to implement the change. "Our mission is to defend this country, and we don't want barriers unrelated to a person's qualification to serve preventing us from recruiting or retaining the soldier, sailor, airman, or Marine who can best accomplish the mission."
Carter also often spoke with pride on his role in speeding the acquisition of armored vehicles for Iraq and Afghanistan during the height of both of those conflicts to better protect U.S. troops from roadside bombs.
Carter served at the 25th defense secretary and "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 a statement. "Carter always set politics aside; he served presidents of both parties over five administrations."
In a statement on Tuesday, President Joe Biden remembered Carter as a man of "integrity."
"When I think of Ash Carter, I think of a man of extraordinary integrity," Biden, who served with Carter in the Obama administration, wrote. "Honest. Principled. Guided by a strong, steady moral compass and a vision of using his life for public purpose."
"Ash was a leader on all the major national security issues of our times – from nuclear deterrence to proliferation prevention to missile defense to emerging technology challenges to the fight against Al Qaida and ISIS," Biden wrote. "He opened every field of military service to women and protected the rights of transgender service members."
The president noted that he relied on Carter's expertise in his own administration as a member of his Council of Advisors on Science and Technology.
"Above all, Ash understood the sacred obligation we have to our servicemembers, veterans, and their families," Biden wrote. "He was relentless in his pursuit of technology solutions for our warfighters, rapidly accelerating delivery of mine resistant vehicles to our troops to protect them from improvised explosive devices in Iraq and Afghanistan. His work saved countless lives and limbs."
"On many weekends Ash and his beloved wife Stephanie would quietly visit wounded warriors at Walter Reed," the president recounted. "He did so out of the spotlight, demonstrating the personal integrity and sense of duty that distinguished him throughout his life."
"Ash Carter was a great American of the utmost integrity," the president concluded. "May God bless him. May God protect the troops Ash Carter served and loved."
In a statement of his own, former President Barack Obama remembered Carter as "a leader who left America — and the world — safer through his lifetime of service."
"Michelle and I extend our heartfelt sympathies to Ash’s wife, children, and all those who loved him," he added.