CIA - United States 

Central Intelligence Agency which was set up post Second World War is the most advanced intelligence agency which scouts the world. The CIA performs covert operations, gathers information from nations and individuals on the request of President. The CIA has done numerous operations which are successful but massively criticized for its failure in 9/11 attack events. Often the US congress blames CIA for violating the human rights but it is one such agency where everyone could rely for anti-terrorists activities. So, this is it about the most sophisticated intelligence agencies. If you know any other agencies which has shown an impact in the history, do comment below.