U.S dollar.

The u.s dollar plays a central role in most traded currency .It comprises of the world official foreign exchange reserves because every investor ,business and central bank own it ,they pay attention to it. The u.s dollar plays a central role in forex market because ,
1.The u.s economy is the largest economy in the world.
2.They are the world sole military super power.
3.The u.s has the largest liquid financial markets in the world.
4.They are the medium of exchange for many cross border transaction.
5.The u.s dollar is the reserve currency of the world.