Who would it be? I would personally pick Wheatley from Portal 2. While kinda a screw-up, he's frickin hilarious.
Edit: Just to clarify, I meant like an artificial intelligence, a machine.
Edit: Cortana seems to be the favorite here (no surprise).
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A cadre of Knights, outfitted with Mythoclasts and stolen technology from the #Destiny-verse to furthermore enhance their capabilities and freedom. These are a kind that will be far more difficult. They are relentless, tireless, and absolutely thorough. [spoiler]Alternatively, an AI version of the Ur-Didact would have many uses, especially when the Logic Plague has been purged from his digitized mind (yes, he did not die, but he hath been composed with the remaining 6 (there were 7!) ).[/spoiler]