I wish I had a Constans Siliqua. Hint: This Emperor was appointed Caesar then became an Augustus. This was rare as not many Emperors after the tetrarchy even bothered with the junior position of Caesar.
Neither Arcadius nor Constantine II. Hint 2: This Emperor made a name for himself by successfully driving the Germans out of Gaul and punishing them severely. The later Emperor Valentinian would serve under this Emperor in the Gaulic campaign.
In light of the two prior guesses, the answer was pretty funny. While I think your Drusus portrait is fairly distinctive (although Germanicus or a more flatteringly portrayed Claudius wouldn't be farfetched guesses), I did remember your coin from prior posts. Staying in an era in which Imperial portraiture maintained some semblance of realism and consistency, here's the next one.