Drew Angerer/Getty Images

On Monday, President-elect Donald Trump officially nominated retired Marine Gen. John Kelly to head the Department of Homeland Security. It was reported last week that Trump would tap Kelly, but Trump had not yet formally offered him the position as Kelly was out of the country.

"Gen. John Kelly's decades of military service and deep commitment to fighting the threat of terrorism inside our borders makes him the ideal choice to serve as our secretary of the Department of Homeland Security," Trump said in a statement. Trump also noted Kelly was "the right person to spearhead" the job of "stopping illegal immigration and securing our borders."

Kelly served in the military for four decades. Before retiring, he was chief of U.S. Southern Command, which is in charge of military operations in Central and South America. Kelly has been critical of President Obama's plans to close Guantanamo Bay and his decision to allow women to serve in combat roles.

Kelly is the third general invited to serve in Trump's White House, alongside retired Lt. Gen. Michael Flynn, who will be national security adviser, and retired Gen. James Mattis, who was chosen to be defense secretary.