JOHN Brennan (pictured) was raised in New Jersey but his parents originally came from Co Roscommon.
Mr Brennan takes over from the highly decorated general, David Petraeus, who resigned following a public scandal in which news of his affair with Paula Broadwell, his biographer, broke.
Mr Brennan is famously proud of his Irish roots and is a regular visitor to the White House on Saint Patrick's Day.
He is credited with redrafting US counter-terrorism policy. The "playbook", as he calls it, is believed to have heavily influenced the administration's approach to taking on al-Qa'ida . Mr Brennan was reportedly headed for the Catholic priesthood when, while on a bus as a student at Fordham University in the 1970s, he stumbled on a recruiting ad for the CIA. He has been in the CIA 25 years.