He's baaaack! Star Wars fans were left with a lot of reasons to be angry after the Expanded Universe was scrapped for Disney to start from scratch (you can't blame them for not wanting to have to adhere to decades worth of novels, video games, and comics), but chief among them was the disappearance of Grand Admiral Thrawn, a villain created by Timothy Zahn in the novel Heir to the Empire.
He took over the Empire following the events of the Battle of Endor in Return of the Jedi, but this version will be making his presence felt in the years covered by Star Wars Rebels. His return is no doubt going to add some weight to theories that he may Supreme Leader Snoke, but regardless of whether or not that's the case, his return is great news. It was also confirmed that Star Wars: Thrawn is being written by Timothy Zahn (which will reintroduce him to canon when it goes on sale in April).
Anyway, check out the Star Wars Rebels trailer below to see him in action for the first time. The character is being voiced by Lars Mikkelsen, the brother of Mads, who will be seen in Rogue One.