Grand Admiral Thrawn debuted in the pages of 1991's Heir to the Empire, the beginning of a beloved series of novels by author Timothy Zahn.
Star Wars Rebels brought the character into the current Disney-owned canon, making him a critical part of the Empire's fight against the emerging Rebel Alliance. Ultimately, he was defeated and pulled into hyperspace alongside Ezra Bridger by the ancient Purrgil.
We've since discovered that they're both stranded in another Galaxy but the only glimpse we've had of Thrawn thus far is in Ahsoka's trailers. It's unclear how significant his role will be in the next few episodes, though we expect the Grand Admiral to be a major part of Lucasfilm's future stories set during this post-Return of the Jedi period.
In a newly released Entertainment Tonight interview from this past April's Star Wars Celebration (via SFFGazette.com), Ahsoka showrunner Dave Filoni reveals why bringing Lars Mikkelsen back as the live-action Thrawn after he voiced the villain in Rebels was the only casting decision he ever considered.
"It was a very big challenge to cast the voice," he recalls. "You know, how do you find a voice for a character that everybody who has read it, pictured it probably in a different, unique way?"
"Eventually, that led me to Lars, and we were all very happy with his performance in Rebels. [Jon Favreau said to me] 'It's going to be very hard to beat Lars.' Because Lars is in my head. The sound of his voice is kind of what I write to."
"[I thought] 'Now it's gotta be Lars' and Jon's like 'Okay.' He looks wonderful in blue. Not everybody does, so that's a factor and we worked on the eyes so...it's a unique thing to bring this character to life." Filoni would go on to praise Mikkelsen's "presence [and] his stature...there are many factors that he's able to deliver on, and I couldn't be happier."
If Thrawn returns from that neighbouring Galaxy, we're guessing he'll bring an army with him in order to take his place as heir to the Empire. How that will tie into the eventual formation of the First Order is hard to say, though we're sure his story will continue into a second season and even Filoni's Star Wars movie.
Set after the fall of the Empire, Ahsoka follows the former Jedi Knight Ahsoka Tano as she investigates an emerging threat to a vulnerable galaxy.
Ahsoka was written by Filoni, who executive produces alongside Favreau, Kathleen Kennedy, Colin Wilson, and Carrie Beck. Directors include Filoni, Steph Green, Peter Ramsey, Jennifer Getzinger, Geeta Vasant Patel, and Rick Famuyiwa.
The first five episodes of Ahsoka are now streaming on Disney+.