King Faisal I was the first King of
Iraq after Britain pieced together what is now
Iraq from
provinces of the old
Ottoman Empire.
The man who united Saudi Arabia is often known simply as King Faisal. Since Saudi Arabian rule does not descend from father to son but from elder brothers (among the sons of King Faisal) to younger brothers, there is no number after his name. Since the British tried to put a constitutional manarchy into place in Iraq, the first two rulers are known as King Faisal I and King Faisal II. They should not be confused with the Saudi Arabian King Faisal.
King Faisal I was an Arabian prince who had fought in the Arab revolt against the Ottomans. He relied largely on officers who had fought with him, and his government favored Sunni muslims over the Shiite majority and the other Kurd minority.
Sources:
Saddam Hussein and the Crisis in the Gulf by Judith Miller and Laurie Mylroie
Also some general knowledge about Saudi Arabia I picked up from several books which I don't have to hand right now, and the everything2 entry on King Faisal.