3B3-21 was a B1 battle droid who served in the Trade Federation Droid Army under Trade Federation Viceroy Nute Gunray. The droid was a part of the invasion force that swept into Naboo's capital city of Theed in 32 BBY, and later defended the Federation-occupied Theed Palace from the planet's leader, Queen Amidala, during the Battle of Naboo. 3B3-21 was later deactivated, along with every other battle droid on Naboo, when the Federation's Droid Control Ship was destroyed.