Monitor droid (Earth-2042)

"Greetings! I am the monitor droid of Installation 04. I am 343 Guilty Spark."

- 343 Guilty Spark

A monitor droid is an advanced droid, or ancilla, created by the Forerunners to occupy special positions in their society. Monitor droids are characterized as being embodied in floating metallic casings.

The Covenant, and as a consequence, the Confederacy of Independent Systems, refered to monitor droids as Oracles; they revered the "Oracles" for their wisdom and believe that they were key to the fulfillment of the Great Journey.

Source

 * https://www.halopedia.org/Monitor