Well, there have been five rulers / dynasties in Germany who managed to acquire big parts of it. The first one was Henry the Lion who rebelled against the emperor, but was defeated. The second one was Ottokar Przemysl, who was also attacked and defeated when he became too powerful for the other princes. The third ones were the Luxemburg dynasty who acquired Bohemia, Silesia and Brandenburg, but lost it again. Number four and five are the Habsburgs and Hohenzollern.
Somehow I think it's not possible to unify Germany early, no matter what you do - after 1250 (the Interregnum), or maybe even before, it was so splintered that nobody could hope to unite it - the other princes, and maybe foreign powers would've stopped him no matter what. Remember, in OTL it took the works of three important men (I don't want to call them great, at least not all of them) to unite Germany (or at least to overcome the old system where the single states have lots of power and the central government doesn't): Napoleon, Bismarck and Hitler. And even today, German länder still have strong rights. That's why I don't think that a single man could do that. Maybe uniting parts of it, making his piece of the cake a bit bigger... repeat that often enough, until there are maybe three states left, but afterwards?
(OTOH, China was very splintered at the beginning until it was united during the spring- and autumn-time and the time of fighting empires... but how did they do it, than?)