Robbie is a self-aware robot. He isn't supposed to be - just became self-aware. His original purpose was to support a time travel expedition, but things went wrong and he ran away. But to be fair, he returned and in his own way - supported the mission.
The trip into the future is not sanctioned by any government agency but received private funding. As such, it was completely 'off the books' and flying below the radar. Secrecy was of the utmost importance and having a rogue, self-aware robot out there and running around didn't help lower the boiling point of several blood pressure readings.

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