Dohring will play Chronos, the God of Time, in this season’s 12th episode, set to air in mid-January. As Chronos is usually an old man with a beard, and Dohring is, well, not, it looks like Supernatural's going in a bit of a different direction with their depiction.
The episode will have a time travel aspect, for which Chronos is responsible (and which probably explains the de-aging). We'll go back in time to meet FBI agent Eliot Ness, who wasn't just a Prohibition-enforcing fed, but also a supernatural hunter. Ness will be played by genre fave Nicholas Lea, aka Alex Krycek from the X-Files.