Short answers, pulled from the story.
Timothy Zahn introduced Grand Admiral Thrawn in the 1991 novel Heir to the Empire. This book marked the first appearance of an alien military leader within the Star Wars franchise.
Grand Admiral Thrawn studied military intelligence alongside the artwork of other cultures to gain psychological insights into enemies. He believed that understanding an opponent's art revealed their true nature and used this method to outmaneuver foes who relied on brute force alone.
In the series finale Family Reunion, and Farewell, purrgil creatures dragged his ship into hyperspace. Ezra Bridger brought the purrgil to defend Lothal while ensnaring Thrawn's vessel, leaving the fate of both unknown after this event.
Disney+ released Ahsoka in 2023 marking the first live-action appearance of Grand Admiral Thrawn. The character appeared in Part Six: Far, Far Away revealing his survival from hyperspace travel.
Lucasfilm rebranded the Star Wars Expanded Universe as non-canon material in April 2014. This decision affected thousands of novels, comics, and video games produced since the original 1977 film.