A new poster has been released for Transformers: The Last Knight that demands you "Rethink Your Heroes". The tag line goes along with the trailer that suggests that Optimus Prime has turned on the Autobots. Things to note is the ships(?) in the background that to me look a whole lot like pirate ships and a bit of Bumblebee's arm on the rock pile.
The other thing to note is the purple eyes of Optimus. Hardcore fans are familiar that this is the sign of Nemesis Prime which as the name suggests is an evil version of Optimus Prime. The character doesn't really have a comics presence. Really he just exists for the toy lines as a black and purple recolor of the same Prime mold. The character concept is based on Star Trek's Mirror Universe concept which TF fans sometimes refer to as the Shattered Glass universe. The core concept is straight forward - the Autobots are evil, the Decepticons are the good guys. Both sides retain their line-ups and logos, they just tend to have different color schemes and their moral code is the opposite of what we know them to be. Since mostly a toy line creation, sometimes Nemesis is Optimus turned evil but often it is a completely separate character.
So from a movie perspective this poster then brings up a few questions. Is this Optimus turned evil or a new character? Is he called Nemesis Prime in the story? As always speculate away in the comments. Thanks to Feris O. for the heads-up. Hi res versions of the poster are available on Michael Bay's flickr account.