Originally Posted by Mr. Dent
It can't be anyone but Thanos. It's not going to be Ultron. All the other villains being introduced in Phase 2 aren't worthy and I doubt they're going to do a Loki redux. The only thing I can see being even slightly viable besides Thanos is if Baron Zemo is in Cap 2 and he gets a Masters of Evil together, which is far less likely than Thanos just being the villain.
Mandarin would be worthy. No?