How many movies have Gertrude Welcker and Thea von Harbou collaborated on?

They have worked on 4 movies together! Their first movie together was Dr. Mabuse, the Gambler: Part 1 – The Great Gambler (1922) while their highest rated movie together was Dr. Mabuse, the Gambler (1922). They have not worked together since The Chronicles of the Gray House (1925). They are most known for their thriller films together.