GlaDOS is a power-hungry AI that's in charge of the whole facility.

Mehrunes Dagon is one of the seventeen Daedric Princes know as 'destruction, change and ambition'. mehrunes dagon's is cold, very hostile, bitter, very arrogant and dominant, mehrunes dagon is also the second most evil Daedra prince and the most dangerous, and his plane of Oblivion, the 'Deadlands',resembles Hell and is inhabited by an army of Demonic creatures called Dremora.

343 Guilty Spark protocol is to contain the flood, remain inside forerunner Installation 04 and may try to trick you to activate the Halo ring to wipe out all sentient life to prevent the flood from spreading

Miraak is a prisoner of the Daedric Prince called Hermaeus Mora. miraak has three dragons name Sahrotaar, Kruziikrel and relonikiv as his slaves. you and miraak meets at the summit of apocrypha