Wotan is an evil sorcerer of great power, who, as Dr. Fate finds out, cannot be killed. Wotan has plagued not only Kent Nelson, but his wife Inza, over the years. Both Kent and Inza have had to deal with Wotan in their respective Dr. Fate states.
Here is Wotan taking Inza prisoner and making the good Doctor's life difficult way back in the 40's.
Wotan's Who's Who description.
It's fitting that both Dr. Fate and Wotan be reintroduced together into the DCnU as they were both introduced in the very first Dr. Fate arc in More Fun Comics. It's nice that James Robinson is giving nods to the original Golden Age stories while putting a modern twist on the stories.