I admit to not having read more than a few dozen issues of his series (due to one particular artist whose style I hated) but should have some idea, surely? Cos arch enemies tend to recur.
DC seem recently to have suggested Deathstroke the Tosser, but he’s more general Titans than Dick. I remember lots of Blockbuster, the smart version. Would it be him? Rapist Tarantula? Ladyshave?
Or do I fall back on Crazy Quilt?
Well, Blockbuster the smart one is (was?) dead, but he could have been in the running. I would still think it is Deathstroke. Yes he is a Titans foe, but he seems to have a specific dislike of Dick.
Yes, considering what happened to Sandy! See "JLA" # 113- The Creature in the Velvet Cage!
Honestly, I'd go with Two-Face -- he and Dick have a fair bit of history, IIRC.