Frederick William IV of Prussia
When revolution broke out in Prussia in March 1848, as part of the European Revolutions of 1848, the king initially decided to fight it with the army, but later decided to recall the troops and place himself at the head of the movement on 19 March.  He committed himself to German unification, formed a liberal government, accepted a national assembly, and ordered that a Constitution of the Kingdom of Prussia should be drawn up. When his position was more secure again, however, he quickly led the army to reoccupy Berlin and dissolved the assembly in December.  But he was still in favour of unification for some time. So the Frankfurt Parliament offered him the crown of Germany on 3 April 1849. He did not accept it, but he tried to establish a union of German states excluding Austria. But rather soon after gave up this plan, when Austria did not accept it.