So far, most of what has been seen of Idris Elba's Krall from Star Trek Beyond paints him as a dangerous and powerful alien. He's come across as a tyrant, enslaving those he overpowers and forcing them to work hard labor. Though he likely had a backstory that would be revealed in the movie, he seemed like a thoroughly bad guy.
A new TV spot shines some light on that past, however, and reveals a side of Krall that we haven't seen before. Not only was he once human (or at least of a human-like race), but he seems to have a grudge against the Federation that dates back to before his transformation.
The spot, titled 'Overwhelmed,' shows the crew of the Enterprise viewing an old recording of Krall before his transformation. The planet he was on had apparently been abandoned by the Federation, and, from the sound of it, was under attack. It's unclear who the attackers were, but from Krall's comments it seems that he didn't expect to survive. He did leave a warning for the Federation in case he did make it through the ordeal, though, and it sounded like he would be out for revenge.
Given Krall's alien form in the previous trailers, one might assume that he was transformed as a result of the attack on his planet. It's possible that he was changed by the creatures that have been seen decimating the Enterprise in the trailers, or possibly even merged with one of them so that he could become powerful enough to orchestrate his revenge against the Federation. That might explain how it seems he's in control of them, though it is of course possible that his "control" is simply a result of the way that the trailers are cut together.
The humanoid version of Krall goes a long way toward making him a more complex villain, instead of the warlord-type that he appeared to be in some of the previous trailers. Parallels might be drawn to Benedict Cumberbatch's Khan who sought revenge against the Federation for the way he and his people were treated, but hopefully Simon Pegg and director Justin Lin aren't quite following the same path with Krall. Revenge can be a powerful motivator, but it's been used as a plot driver in both of the Kelvin Timeline movies so we can hope that Beyond has some new tricks up its sleeve.
Even with this new look at Krall, some fans will obviously prefer the original timeline to anything in the new films. With any luck, though, Star Trek Beyond will benefit from Pegg and Lin's work and will give even some of the new films' critics something to enjoy.
Star Trek Beyond opens on July 22, 2016.