– Donald Trump formally picked John Kelly on Monday to lead the Homeland Security Department, putting an outspoken retired Marine general in charge of delivering Trump's promised crackdown on ­illegal immigration.

Kelly, who lost a son in combat in Afghanistan, is the third recently retired general to join Trump's Cabinet. Like the others, he clashed at times with the Obama administration.

If confirmed by the Senate, Kelly will be tasked with carrying out some of Trump's most controversial campaign pledges, including building a wall along the border with Mexico, boosting deportations of immigrants in the country illegally and vetting visitors from Muslim-majority nations.

"He is the right person to spearhead the urgent mission of stopping illegal immigration and securing our borders, streamlining [the Transportation Security Administration] and improving coordination between our intelligence and law enforcement agencies," Trump said in a statement.

Kelly, 66, said he was "humbled and grateful" to be picked.

"The American people voted in this election to stop terrorism, take back sovereignty at our borders and put a stop to political correctness that for too long has dictated our approach to national security," he said in a statement.

"I will tackle those issues with a seriousness of purpose and a deep respect for our laws and Constitution. I am honored for the opportunity to be back in the service to our country and our people."

Kelly, a Boston native, enlisted in the Marine Corps in 1970 and was discharged as a sergeant in 1972. He was commissioned as an officer after he graduated from the University of Massachusetts in 1976.

Since then, he has commanded Marines from platoons through corps level and combatant command, including multiple tours in Iraq.

He also is a veteran of bureaucratic and political battles in Washington.

He served as the Marines liaison officer to the House of Representatives, and then later to the entire Congress. He later served as a senior military assistant to Defense Secretaries Robert Gates and Leon Panetta.

Beginning in late 2012, he headed the U.S. Southern Command, the Pentagon's regional headquarters for operations in the Caribbean, Central America and South America.

Kelly retired in January as a four-star general, the first since the Korean War to be promoted to that rank while in active combat.

He had a more painful distinction as the highest-ranking U.S. military officer in years to lose a son or daughter in combat.

His son, Marine Lt. Robert Kelly, was killed by a land mine in 2010 while he was leading a Marine platoon against the Taliban in southern Afghanistan.

By choosing the retired general, Trump signaled a more militarized approach to border security after railing on the campaign trail about growing risks on U.S. borders.

As head of the Southern Command, Kelly ordered military operations in the Pacific Ocean and the Gulf of Mexico to try to stop drug smugglers. The role made him an attractive candidate to Trump's transition team.

If confirmed, Kelly will run a department that has struggled with management and morale problems since its creation after the terrorist attacks of Sept. 11, 2001.

It includes 22 agencies and nearly 250,000 federal employees who protect the president, tell airline passengers to remove their shoes, deliver aid after natural disasters, patrol on horseback along the border and do numerous other jobs.