O-Lir was the last Sentinel of the Sanctuary Fortress Temple on Aether. Samus encounters the message left by O-Lir via Luminoth Holoprojector in the Sanctuary Energy Controller chamber. The message reveals that it was O-Lir who constructed the many mechanoids patrolling the fortress to fight the Ing, whose Hive was the dark representation of the Sanctuary. Slowly, the Ing possessed them and turned them against their Luminoth creator, using them as guards in their heavily protected Hive. The hologram programs Samus's Translator Module to read Cobalt holograms. O-Lir died filled with regret for the corrupted inventions and with fallen honor; the Sentinel ends the message with the usual Luminoth expression of goodwill.
In subsequent messages, O-Lir makes reference, directly or indirectly, to the Spider Ball, Power Bombs, the Echo Visor, and the Annihilator Beam. O-Lir's hologram is last seen appearing spontaneously to bow in thanks to Samus after she returns the Light of Aether to the Sanctuary Energy Controller.
A corpse presumed to be O-Lir's is discovered in the Sanctuary Energy Controller by Samus. Information collected from it indicates that O-Lir died some 1.1 decacycles prior to her arrival and was damaged by Luminoth weaponry, presumably rogue mechanoids that could overtake the warrior where the Ing could not.
- "Hear the words of O-Lir, last Sentinel of the Fortress Temple. May they serve you well." —O-Lir's Hologram (Metroid Prime 2: Echoes)
- "This used to be a great fortress, a safe haven for our people during the war. It also holds portals to the Ing Hive, the heart of their dark tribe. During the war, I built a number of mechanical sentinels to join me in battle. They were made to fight the Ing, and fight them they did...for a time." —O-Lir's Hologram (Metroid Prime 2: Echoes)
- "One by one, the Ing corrupted them. Now, they attack with no mercy. Many went to Dark Aether with their Ing masters. Expect them when you are in the Hive. The Ing like to use them as guards. The Ing will protect their home with great ferocity. In all of our battles, the Hive has never fallen." —O-Lir's Hologram (Metroid Prime 2: Echoes)
- "I have updated your Translator Module. You can access devices and door coded with Cobalt holograms. Search the areas now open to you." —O-Lir's Hologram (Metroid Prime 2: Echoes)
- "If only I could join you...redeem my fallen honor in battle. But, my time has passed. Good luck. Let the Light of Aether show you the way!" —O-Lir's Hologram (Metroid Prime 2: Echoes)
- "The machines travel on a network of magnetic rails. They go to places you cannot reach. It’s a pity I didn’t have the time to craft a way for people to use these rails as the machines do." —O-Lir (Metroid Prime 2: Echoes)
- "The machines have fashioned a new alloy of considerable strength. They use this metal to block access to key areas. Destroy it if you can!" —O-Lir (Metroid Prime 2: Echoes)
- "The last of our champion’s visors used sound to target the unseen. Recover it from its place of honor and use it wisely!" —O-Lir (Metroid Prime 2: Echoes)
- "The strongest weapon of our champion is in the hands of the enemy. It fires a blast of light and dark energy, and has no equal. Find it soon!" —O-Lir (Metroid Prime 2: Echoes)
- "Bioscan complete. Luminoth subject terminated 1.1 decacycles ago. Subject has taken damage from a number of Luminoth weapon systems, most likely those used by rogue Luminoth combat drones. It took more than the Ing to defeat this warrior." —Scan Data (Metroid Prime 2: Echoes)