By Your SideG 15

This achievement is unlocked by acquiring your first companion. Companions are helpers that you can summon and will fight with you in your adventures. Once you reach level 16 Sergeant Knox in Protector's Enclave will give you a quest directing you to your first companion. This quest is not required to use the companion system as companions can also be acquired via trade, auction, zen store, promotion, or other means. If you one of these other means then the companion can be used as soon as your character completes the basic game tutorial at the beginning of the game.