TX-21 was a T-series tactical droid who served under Geonosian Archduke Poggle the Lesser in a droid foundry on Geonosis. TX-21 informed Poggle that ten garrisons of ready battle droids were ready to be deployed. He said the Republic would not be able to destroy the new super tanks. When he learned about the Padawan intruders in the factory, Poggle, TX-21, some Geonosians and a super tank piloted by B1 Battle Droids came to stop them. Ahsoka threw a detonator at the super tank, stationed next to TX-21. The droid laughed and explained that the tank could not be destroyed, however, when the bomb activated, indeed the tank was unharmed, but TX-21 was destroyed.