What is the name of the ancient Forerunner AI encountered in Halo: Combat Evolved?

The ancient Forerunner AI encountered in Halo: Combat Evolved is 343 Guilty Spark.

343 Guilty Spark is a Forerunner Monitor assigned to Installation 04. He guides Master Chief through parts of the ring and explains the installation’s containment systems, initially presenting himself as an ally in the fight against the Flood. His spherical design and formal speech make him one of the most recognizable Forerunner characters in the series.

Guilty Spark’s objectives are tied to activating and protecting the Halo installation. The story later reveals that firing the ring would destroy sentient life across the galaxy in order to starve the Flood. Master Chief and Cortana therefore turn against the Monitor’s plan and destroy Installation 04 instead.

The number in his name is important because Halo has several Monitor characters with different numerical designations. 2401 Penitent Tangent is associated with Installation 05, while 000 Tragic Solitude is associated with the Ark. Those characters should not be confused with 343 Guilty Spark.