Retired Gen. John Kelly was in the military for 45 years - a very long time, even for a general, and if the Senate confirms him, he'll be in service even longer still.
Kelly was once
the head of US Southern Command, putting much of the US' immediate vicinity under his purview -- including the control of Guantanamo Bay. Trump has pledged the US will redouble its focus on its southern border and overhaul its approach to terror threats.
Given Kelly's knowledge of the southern theater and his extensive military experience, he would be poised to help Trump deliver on his campaign promises from a position atop DHS.
What do Kelly's critics say?
Much of the pushback against Kelly is driven by the same logic animating criticism against his Trump's approach to immigration and terrorism: That is, for people who view Trump's policies as overzealous and even draconian, Kelly would be a strict enforcer.
Kelly's past statements and experiences, especially overseeing Guantanamo Bay, indicate to many that Kelly will do little to temper Trump's heated promises.
The DHS chief has more of a role in implementing policy than forming it, so Kelly could effectively marshall the department's vast resources to realize some of Trump's most controversial policies -- from deporting millions and militarizing the border with Mexico to implementing anti-terror measures targeted at Muslims.
Kelly lost his son in Afghanistan
Like Trump's pick for secretary of defense, retired Gen. James Mattis, Kelly is a Marine.
The Marine Corps shaped much of his life, and he rose through its ranks to become one of the country's top military leaders.
But the military also shapes his life in another, personal and tragic way. Kelly is a gold-star father. His son was serving in Afghanistan when he was killed in action, leaving Kelly and his wife the parents of a soldier slain in the war on terror.
The death of Kelly's son contributed to his view of service and the general public's attitude towards the military.
In a speech
he gave to fellow gold star parents in 2012, Kelly said of his son: "He had decided somewhere between the day he was born and 07:19, 9 November 2010, that it was worth it to him to risk everything -- even his life -- in the service of his country."
Kelly retired in January 2016, so depending how the confirmation process goes, Kelly will not have been retired for long.
He has been known to speak in graphic and blunt terms about threats he believes the US faces.
In a 2013 speech, he said
of terrorists: "I don't know why they hate us, and I frankly don't care."