Blue-Tark was a feminine T-series tactical droid that served under Master Geneticist Zeta Magnus. In 22 BBY, during the first weeks of the Clone Wars, the droid was stationed within the citadel of Marat V during her master's conquest of the planet. Assisting the clone of Zeta Magnus as he controlled the planet as a proxy for his progenitor and creator, Blue-Tark fled the citadel in the wake of the revolt by the native S'kytri, maiming the clone in the process as he stood in the wake of the droid's ship's engines. Returning to her true master in the heart of the Dark Worlds at the Rennek palace, she reported to him of the loss of the world at the hands of the Jedi.
Concept art of Kenner's "Blue-Four"
Blue-Tark was originally designated as Blue-Four in Kenner's canceled The Epic Continues toy line. Originally created to serve as the personal attendant of Atha Prime, he was meant to pilot Prime's starfighter Apex Invader in battle. He was renamed Blue-Tark for Abel G. Peña's SkyeWalkers: A Clone Wars Story, with Tark translating to the word four in the Thyrsian tongue. Like wise, Blue-Tark's master was an analogue of Prime, renamed Zeta Magnus, and flew the Skyriver Invader.
According to Peña's endnotes for SkyeWalkers, Blue-Tark's full designation is TB-1U4, although this name was not provided in the story itself.