U.S. President Barack Obama is turning to a long-time aide to fill one of the most influential positions in Washington.
Obama named key adviser Denis McDonough on Friday as his fifth chief of staff.
McDonough previously served as a White House foreign policy advisor. He was one of the aides photographed with Obama as the president watched the U.S. special forces raid that killed al-Qaida leader Osama bin Laden in May 2011.
Obama called McDonough indispensable, saying he is "a great friend to me and everybody who works here at the White House."
"He's been one of my closest and most trusted advisers on my presidential campaign, on my transition team, he has been an indispensable member of my national security team, as well, said the president," said the president. "Denis has played a key role in every major national security decision of my presidency, from ending the war in Iraq, to winding down the war in Afghanistan, from our response to natural disasters around the world, like Haiti and the tsunami in Japan, to the repeal of 'Don't Ask, Don't Tell,' to countless crises in between, day and night."
McDonough takes over for Jack Lew, who has been nominated to be secretary of the Treasury.
The White House also announced several other staff changes Friday.
Separately, a federal appeals court ruled Friday that three of the president's appointments to a federal board were unconstitutional.
Obama made the appointments to the National Labor Relations Board a year ago while the Senate was not in session.
A White House spokesman called the ruling "novel and unprecedented." Jay Carney said it contradicts 150 years of practice by both Democratic and Republican administrations.
In the past, U.S. presidents have used so-called "recess appointments" to bypass the Senate, as the chamber will sometimes try to block a president's nominees.
In this case, the appeals court ruled the recess appointments were not valid because, although the Senate was not meeting, lawmakers were still available to act on the nominations.