Assistant to the President for Homeland Security and Counter-terrorism, John Brennan, is one of the masterminds behind the assassination of Osama Bin Laden.
Mr Obama views him as his right-hand man on international relations.
Mr Brennan's father is from Roscommon and his mother from Galway. He said it was an honour to address the Irish Institute of European Affairs in Dublin yesterday.
"The national security team of Tom Donilon, Denis McDonagh, Mike Mullen, Bill Daley and Mount Anville- educated Samantha Power. They are proud Irish citizens. The 'Irish mafia' we are called in the White House."