Gen. Mark Milley bid farewell Sept. 29 after serving as the 20th chairman of the Joint Chiefs of Staff for the past four years.

Milley became chairman on Oct. 1, 2019, after serving as the 39th Army chief of staff. During his tenure as the nation’s highest-ranking military officer and principal military adviser to the president, defense secretary and National Security Council, he helped lead the U.S. military through several pivotal, critical events, including a pandemic, the U.S. withdrawal from Afghanistan, the Jan. 6 attack on the U.S. Capitol and the Russian invasion of Ukraine.

During a farewell tribute Sept. 29 at Joint Base Myer-Henderson Hall, Virginia, President Joe Biden praised Milley for his unwavering service. “As commander in chief, I’ve relied on Mark’s counsel because I know he always gives it to me straight, no matter what,” Biden said. “During his tenure as chairman, Mark has been the steady hand guiding our military.”

Milley was critical to building partnerships around the world, keeping the force at the “cutting-edge of the fields of space and cyber,” standing with the people of Ukraine and more, Biden said. “You’ve given remarkable service to our country,” the president said.

Defense Secretary Lloyd Austin, a retired general who also served with Milley while in uniform, said the retiring chairman “never hesitated to charge into danger for his troops or his country.” During his tenure as chairman alone, he has led while taking on the pacing challenge of the People’s Republic of China, confronting a once-in-a-generation pandemic and leading the world to help Ukraine after Russia’s invasion, Austin said.

“Gen. Milley is a scholar and a warrior,” Austin said. “We respect him for his wits, but we love him for his heart, and he’s thrown his whole heart into leading this tremendous joint force.”

As he retires after more than four decades of military service, Milley will be succeeded as Joint Chiefs chairman by Air Force Gen. Charles Brown, who most recently was the Air Force chief of staff.

In his remarks, Milley said he is humbled to have served as the 20th Joint Chiefs chairman.

“The joint force is the most lethal and capable in the world, and our enemies know it,” Milley said. “We are currently standing watch with a quarter of a million troops deployed in 150 countries.”

In the past four years alone, the U.S. military has conducted “countless” operations and exercises around the world, supported Ukraine, maintained stability in Asia, fought terrorists in the Middle East and Africa and supported the nation as it battled the COVID-19 pandemic, Milley said.

Milley had a special message for those who served in Afghanistan. “Be proud that you’ve protected this country for 20 consecutive years at great cost,” he said. “Hold your head high. You served, you did what your country asked, and each of you served with honor, courage, skills and dignity. Never forget that.”

A Massachusetts native, Milley graduated from Princeton University in 1980. He has served in multiple command and staff positions, including commanding the 10th Mountain Division, III Corps and Army Forces Command.

A veteran of multiple deployments to Iraq and Afghanistan, Milley also has served in the Sinai, Panama, Haiti, Bosnia-Herzegovina, Colombia, Somalia and South Korea.

As Army chief of staff and later as Joint Chiefs chairman, Milley has repeatedly warned of a rapidly shifting geopolitical landscape and the quickly evolving character of war. He also has pushed the Army and the other services to transform to maintain a technological edge over America’s adversaries.

Milley also has repeatedly talked about the importance of the Constitution, especially to those who serve in uniform. Calling it the “moral North Star,” Milley said the Constitution “gives purpose to our service … [and] purpose to our lives.”

The U.S. military is unique because it doesn’t take an oath to a country or a tribe or a religion, Milley said. Nor does it swear an oath to a king, queen, tyrant or dictator, he said.

“Each of us commits our very lives to protect and defend that document, regardless of personal price, and we are not easily intimidated,” Milley said.