Daniel Kinahan, 49, has been charged with directing organised crime following his extradition to Ireland on Sunday. His first full day inside Portlaoise prison on Monday marked a significant change from his previous lifestyle in the United Arab Emirates.
The alleged leader of the Kinahan organised crime group is confined to a cell for approximately 20 hours a day. He is the sole prisoner on a landing in A block, which typically houses eight inmates.
Kinahan was flown to Casement aerodrome on Sunday in an Irish government jet and subsequently taken to the criminal courts of justice in Dublin, where he was charged. He is scheduled to return to a non-jury court on 5 October.
The US had previously offered a reward of up to $5m (£3.7m) for information leading to his arrest or conviction. The US Treasury Department stated that the Kinahan group had been involved in a gang war in Ireland and Spain, which resulted in numerous murders.