Retiring Chairman of the Joints Chiefs of Staff, Army General Mark Milley (L), greets incoming Chairman, Air Force General Charles Brown, during the Armed Forces Farewell Tribute in honor of Milley, at Joint Base Myer-Henderson Hall in Arlington, Virginia, on September 29, 2023.

Top U.S. general Mark Milley will retire on Friday after a four-year tenure that saw successes like the killing of ISIS head Abu Bakr al Baghdadi and helping Ukraine to defend against Russia's invasion, but also included the chaotic withdrawal from Afghanistan and a rocky relationship with former President Donald Trump.

Milley will hand over command to Air Force chief General Charles Q. Brown, who will be only the second Black officer to become chair of the Joint Chiefs of Staff, after Colin Powell two decades ago.