President Obama announced on Friday that Denis McDonough will replace Jack Lew as his Chief of Staff, as Lew has been nominated to replace Timothy Geithner as Secretary of the Treasury.

McDonough, who is currently Deputy National Security Advisor, has been one of Obama’s closest advisors for over a decade. In the early 2000s, he worked for former South Dakota senator Tom Daschle, where he helped round up the votes to pass the Iraq War resolution — something he reportedly regrets. Since then, McDonough has worked to end the wars in Iraq and Afghanistan.

According The Week‘s Mark Ambinder, the president trusts McDonough more than just about any other advisor. The Chief of Staff plays a crucial role in the White House as a gatekeeper of the president’s time and attention.