Every now and then a writer announces that an obscure villain will have a big role in an upcoming story. For example, Gage recently revealed a villain who hasn't been seen since 1979 will appear in a future issue of Amazing Spider-Man. Libra had a major role in Final Crisis, 30+ years after his sole appearance in a Justice League two-parter.
In that vein, what obscure villain would you like to see pop up again?