Gen. John F. Kelly, the retired four-star Marine general sworn in Monday as White House chief of staff, has new orders from the commander-in-chief: Instill discipline in a White House plagued by leaks and infighting.

Kelly, an Irish Catholic, had a brief stint as secretary of Homeland Security. Before he headed DHS, he had recently ended a long and distinguished career in the military.

Last February, he retired after serving four decades in the Marines. His last post was as head of the U.S. Southern Command, which oversees Latin America and the Caribbean.

"I have been fortunate to have served my country for more than 45 years - first as a Marine and then as the Secretary of the Department of Homeland Security," Kelly said in a statement Friday. "I am honored to be asked to serve as the chief of staff to the president of the United States."

In a tweet late Friday, Trump tweeted that Kelly "has been a true star of my administration."

“He is a great American and a great leader,” Trump said.

Kelly, who vehemently defended Trump’s travel ban, has grown close with the president the past few months.

The Washington Post said Trump is “drawn to the discipline that Kelly and his other advisers who are former military officers bring to their roles.”

He is also allegedly close to both White House chief strategist Stephen K. Bannon, and liked by Trump’s son-in-law, Jared Kushner. He’s described as low-key and a good collaborator.

His selection Friday was greeted with praise on Capitol Hill.

“Secretary Kelly is one of the strongest and most natural leaders I’ve ever known,” said South Carolina GOP Sen. Lindsey Graham, who has sparred with the president in the past. “As a Marine Corps officer, he instilled loyalty, respect and admiration from all who served under him.”

Speaking to reporters, White House Press Secretary Sarah Huckabee Sanders cited Kelly’s role at the Department of Homeland Security in working to reduce illegal immigration.

“He has helped seal the border and reduced illegal immigration by 70 percent,” Sanders said. “He is respected by everyone, especially the people at the Department of Homeland Security.”

A profile in the Boston Globe when he was chosen by Trump to head DHS mentioned a powerful speech he delivered in Massachusetts honoring service members in the state killed since the Sept. 11, 2001 attacks.

He spoke to the crowd but never mentioned that his own son was killed in Afghanistan three weeks prior.

"He was probably torn up inside," Chris Lessard, a Newton firefighter and Marine veteran, told the Globe. "That was my first impression of General John Kelly. Could you find a classier person? He's a great man."