Former Pentagon chief Ash Carter, who was instrumental in the US-led fight against ISIS in Iraq and Syria and who helmed the Department of Defence for two years under Barack Obama, has died, his family said on Tuesday.
Carter was Mr Obama's fourth and final defence secretary, serving until he was succeeded by Jim Mattis in 2017.
“It is with deep and profound sadness that the family of former secretary of defence Ashton B Carter shares that Secretary Carter passed away Monday evening in Boston after a sudden cardiac event at the age of 68,” the family statement read.
President Joe Biden, who was vice president when Carter was secretary of defence, celebrated his late colleague's "steady moral compass". Mr Biden said that, after he was sworn into office as president, he continued to rely on his expertise.
"Above all, Ash understood the sacred obligation we have to our servicemembers, veterans and their families," Mr Biden said, crediting the former defence secretary with saving "countless lives and limbs".
Mr Obama said he relied on Carter as the US pursued a more humane and effective long-term military strategy. Carter, he said, was instrumental in accelerating US counter-terrorism efforts, strengthening allies and opening combat roles for women.
"Ash's greatest legacy however, may be the generations of younger leaders he taught, mentored and inspired to protect our nation and wield power wisely," Mr Obama said in a statement.
After leaving public service, Carter led the Belfer Centre for Science and International Affairs at Harvard's Kennedy School.
Carter originally trained as a physicist at Oxford University, earning a doctorate in theoretical physics in 1979. During lengthy overseas flights with reporters on trips as Pentagon chief, he would sometimes discuss the building blocks of the universe.
During his lengthy time in public service, he pushed for technological development within the Pentagon, including the creation of tech hubs to boost private expertise in the Defence Department.
“Carter always set politics aside; he served presidents of both parties over five administrations, holding multiple positions within the Department of Defence,” his family said in the statement.
He served under Bill Clinton from 1993 to 1996 as assistant secretary of defence for international security policy and supported the efforts of a newly independent Ukraine to give up its former Soviet nuclear arsenal.
Before becoming defence secretary, Carter served as deputy defence secretary and chief operating officer in the Pentagon, where many viewed him more as a technocrat offering steady leadership while Mr Obama finished out his final term.
As secretary of defence, Carter helped Mr Obama carry out the initial “pivot to Asia” that aimed to take on China as a great commercial power and military competitor.
But the rise of ISIS in 2014 drew America's attention once more to the Middle East, and Carter helped build up Operation Inherent Resolve, the international coalition that eventually liberated territory held by the terror group across Iraq and Syria.
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.
The following year, Carter was responsible for ending the ban on transgender troops in the US military. Mr Trump in June 2017 blindsided the Pentagon and announced on Twitter that he would again bar transgender troops from serving.
