By Anadya Narain
The 'Oppenheimer' star is very private when it comes to his family and personal life so here is some information which he has revealed about himself over the years.
Cillian was born in Cork in 1976, his mother taught French and his father worked as a school inspector.
Cillian was in a band with his brother called The Sons of Mr. Green Genes bandmates, along with other members and they were even offered a five-album record deal.
However declining the deal, he later went on to study law at University College Cork before he dropped out in an effort to break out into the world of acting.
Cillian found success as an actor, appearing in late 90s Irish film Disco Pigs and Danny Boyle's violent horror 28 Days Later in 2002.
He married Irish artist Yvonne McGuinness in 2004 and they have two children together, Aaron and Malachy.
Cillian and his family now live in Dublin, a Victorian townhouse which he bought for £1.7million.
Margot Robbie Hated What The Beatles Did to Her Favorite Band, Refused Listening to Them Out of Revenge for ‘Stealing the limelight’