Wolfenstein/Wevelsburg and King Arthur and the holy grail?

This documentary is about Wevelsburg which is an EXCELLENT but creepy museum. It also contains the SS cultbeliefs which appearantly also included King Arthur and the Holy Grail. Unlike the ancient game Wolfenstein zombies are not included. (I knew Paderborn was a real place but didn’t know the Castle actually inspired the game).

But trying to be serious about this lunacy I always wondered what drove the National Socialists to invent their own religion or was it a founding myth? Does anyone have reliable source for this.

See minute 3:50

PS Like said a great museum and free to visit.