Andreas Cornelis (Dries) van Kuijk was born Dutch. He joined the U.S. Army and changed his name to Tom Parker. He worked in carnivals and later took on the "Colonel" nickname. He had a management company with Hank Snow, but signed Elvis and split with Snow (some have claimed "stole" from Snow).
He never formally acquired U.S. citizenship, so some speculate that he feared to leave the U.S. for fear of being denied reentry. Others have speculated that the Colonel might have murdered someone in the Old Country or committed some other kind of crime that might have come to light and prevented him from getting a Visa or citizenship.
So that's why Elvis seldom played outside the U.S. When he played in Canada, the Colonel stayed on this side of the border.