The White House praised Lieutenant General H.R. McMaster as a "terrific person'' on his last day as national security adviser.
Press secretary Sarah Huckabee Sanders paid tribute to McMaster, who is leaving after just over a year in office. He'll be replaced Monday by John Bolton, a former ambassador to the United Nations.
Sanders said it had been "a real privilege'' to work with him.
Trump told McMaster last month he wanted a change in his foreign policy team. They differed on policy and never developed a strong personal relationship.
Trump was still fond of McMaster and had hoped to find him a suitable place in the military. But McMaster said he was retiring from the Army.
This story was written by the Associated Press.