Hard to tell. It could have been his stage work that got him the role in Steven Spielberg's "Band of Brothers". That would have put his name out there internationally. The BBC's "State of Play" Or through "Shameless" a C4 programme were high profile and successful. But what ultimately put him on the map IMO is "The last king of Scotland".
He is my very favorite actor at this time... he was amazing in Atonement and Last King of Scotland. Personally I hate 'Wanted' but that movie definitely drew some attention to him.