When the Legends canon came into being for the Star Wars expanded universe, many were weeping all that was lost from Star Wars lore. For years, all people had for new Star Wars storylines was featured in the books, comics, and other video game properties. Characters were introduced and fans fell in love with them, including mainstays like Mara Jade and Grand Admiral Thrawn.
The status of those characters was in limbo for a bit, until now. During our visit to the Star Wars: Rebels panel at the Star Wars celebration, it was revealed that Thrawn will be making his return to the main canon as a villain on Rebels.