Frederick William IV of Prussia
In the beginning of his reign he did not continue the reactionary policies of his father, he reduced press censorship and promised a constitution, but he did not want a popular legislative assembly, but preferred to work with the aristocracy. He was Lutheran, but he released the imprisoned Roman Catholic Archbishop of Cologne, and he decided to help the construction of Cologne Cathedral.  In 1844, he attended the celebrations of the completion of the cathedral, so he was the first king of Prussia who entered a Roman Catholic building.  When he finally called a national assembly in 1847, it was not a representative body, but rather a United Diet which cold speak for all the provincial estates and had the right to grant taxes and loans but no right to meet at regular intervals.