The Judiciary Act of 1789 created the Office of the Attorney General which evolved over the years into the head of the Department of Justice and chief law enforcement officer of the Federal Government. The Attorney General represents the United States in legal matters generally and gives advice and opinions to the President and to the heads of the executive departments of the Government when so requested.
That doesn’t mean the AG is the President’s personal lawyer. That’s the Office of Counsel to the President.
The Counsel’s Office also helps define the line between official and political activities, oversees executive appointments and judicial selection, handles Presidential pardons, reviews legislation and Presidential statements, and handles lawsuits against the President in his role as President, as well as serving as the White House Contact for the Department of Justice.