James Mattis
© Jonathan Ernst / Reuters
Shortly after President Donald Trump was sworn in, the Senate confirmed retired Marine General James Mattis as the secretary of the Department of Defense. Later, they also confirmed retired General John F. Kelly as secretary of homeland security.

Also known as "Mad Dog" Mattis, the 66-year-old becomes the first top military officer to serve as secretary of defense since President Harry Truman's appointment of Army General George C. Marshall in 1950.

The Senate voted 98-1 on Friday to confirm the nominee, the first official Trump administration Cabinet member. Senator Jeff Sessions (R-Alabama) abstained from the vote, as he has been nominated as member of Trump's Cabinet.

One of Trump's first official acts as president was signing a waiver Congress approved to allow Mattis to serve in his new role. Typically, defense secretaries must have been out of the military service for at least seven years, as it is a civilian post.

Mattis testified to the Senate last week that Russia was a "principal threat". He also told the confirmation hearing that he disagreed with Trump's position to recognize Jerusalem as the capital of Israel, and called NATO "the most successful military alliance probably in modern history, maybe ever."

The Senate also confirmed retired General John F. Kelly to head the Department of Homeland Security. Senators voted 88-11 to approve Kelly, who left the Marine Corps in January. His last post was as the head of US Southern Command.

Kelly also previously served as an adviser to former Pentagon chiefs Leon Panetta and Robert Gates.

During his confirmation hearing last week, he told senators that he agreed "with high confidence" with the Office of the Director of National Intelligence report accusing Russia of interfering with the US presidential election. He also said that "a physical barrier in and of itself" won't protect the US border with Mexico, and that patrols would still be needed.