O

 is a character in Torment: Tides of Numenera.

Background
An odd "person" sitting in the Fifth Eye, O states, it is something like an ultraterrestrial, but far more. It is a Word, a letter. It is a manifestation of the underlying forces of the universe, what it would describe itself as "superpositional extraction of fundamental universal laws made tangible". It is eternal, has witnessed the birth of the universe and, again, will see its end. However, it is unable to know how it was created.

It showed up at the Fifth Eye to observe the last attempt of the Adversaries to gain access to the Ninth World, through their defeat against the Last Castoff. This will stall them for an aeon and, thank to their departure, Leto's prescience won't be blinded anymore.

O can only be seen by the Last Castoff, whose mind and perception impose it a particular form. After their conversation it disappears, never to return.

Behind the scenes
O first appeared in Planescape: Torment, in the Smoldering Corpse Bar – a location similar to The Fifth Eye. Knowing its nature, it is safe to assume that it's the same person in both games.

Its lines "[…] yours is a true story." and "It was born from desire […]" are probably a reference to the crowfunding campaign for Torment: Tides of Numenera.