This is because Thrawn is much easier to pronounce compared to his full name, which is "Mitth'raw'nuruodo". To that end, "Thrawn" is what's known by the Chiss as Mitth'raw'nuruodo's "core name".

This book kicked off author Timothy Zahn’s trilogy of bestselling books that introduced Grand Admiral Thrawn to Star Wars fans. Jade was the other major character introduced, and she quickly ...