The designation "Immortal" was conceived by Yrica Quell, a double agent for the New Republic embedded within the Galactic Empire's 204th Imperial Fighter Wing, as a potential moniker for the Unyielding, an Imperial-class Star Destroyer under the command of Imperial Colonel Madrighast, during the events of 5 ABY.
Alexander Freed included the Immortal in his 2021 novel, Victory's Price, which serves as the third book in the Star Wars: Alphabet Squadron trilogy.