From Halopedia, the Halo wiki
The Warden was a Forerunner monitor serving aboard the Capital. It was placed in charge of detaining accused criminals before they were judged by the Council, as well as providing their defense. It was an ancient AI, over 25,000 years old by 97,445 BCE.
The Warden was assigned to defend Faber, the Master Builder, before the Supreme Mantle Court during Faber's trial for the misuse of a Halo. During the subsequent attack on the Capital by Mendicant Bias, the Warden aided Faber in escaping, delivering him to Sharp-by-Striking. According to Faber himself, the Warden acted out of its own initiative and saved him because it knew his value; however, when interrogating the Master Builder years later, the Master Juridical asserted that the Warden had been bribed. Faber denied this, stating that the notion of bribing a machine was absurd.
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