The Sentinel is encountered during the mission The Beginning of the End. Little information about the Sentinel is presented until Jack's Vault Hunters enter the Vault and encounter it themselves. Upon arrival inside the Vault, it appears from a portal and must then be defeated twice. First in its humanoid form, then in a gigantic form called The Empyrean Sentinel.
- Main article: The Beginning of the End
- After completion of the main story, the Sentinel can be fought repeatedly in its original form, by returning to the Vault in Eleseer.
The Invincible raid boss version can be unlocked by completing the The Bestest Story Ever Told mission.
- The Sentinel bears great resemblance to the Asuras found in Buddhist texts. Asuras are the lowest form of deity - wicked, multi-faced beings obsessed with the vices of the world.