Simplify the following text for a Grade 4 native English-speaking person.
Original: A Gauleiter was the party leader of a regional branch of the NSDAP ( more commonly known as the Nazi Party ) or the head of a Gau or of a Reichsgau .
Simplified: A Gauleiter was the party leader of a regional branch of the NSDAP . This persons were the head of a Gau or of a Reichsgau .