Chances are you've watched the stunningly awesome Avengers: Age of Ultron trailer a dozen times by now. Well I've probably got you beat there, and every single time the moment that has me geeking out the most is the brief appearance by mo-cap wizard, Andy Serkis. It's notable because he's not playing a CGI creature like Gollum in The Lord of the Rings or a despotic ape like in Dawn of the Planet of the Apes. He's just himself, and that makes Marvel's secrecy around his character all the more intriguing.
While this amounts to a lot of guesswork, the gang at Cinemablend come up with a decent theory that would suggest the first appearance of Black Panther. According to the site, and this is pretty undeniable, Serkis bears a striking resemblance to the Black Panther villain, Ulysses Klaw. Klaw is an expert in the field of sonics, and he's often seen in the Panther's home nation of Wakanda trying to steal the rare metal Vibranium. It's a substance that only exists in Wakanda and is the substance Captain America's shield is partially made of. Virbranium has the power to absorb kinetic impact, soundwaves, and vibrations. There's another scene in the trailer where it looks like Ultron is being forged out of some kind of metal, which could very well be Vibranium. The metal has already appeared in Captain America: The First Avenger, when it was revealed that Howard Stark used it to construct Cap's shield.
It's a solid theory, and I'd be lying if I said it didn't cross my mind that Ultron would be made of Vibranium somehow. In the comics he's mostly forged out of indestructible Adamantium (Cap's shield has it, too), but Marvel can't use it because that's also what Wolverine is made out of, so it falls under 20th Century Fox's rights. Vibranium should make for a pretty good replacement.
Avengers: Age of Ultron opens May 1st 2015.