Can you get Legion early legitimately? I thought it required modding the PC version.
Or by 'early', do you just mean doing nothing but main quests then taking him on all the loyalty/side missions and damn the Normandy crew? Because there is unused dialogue for him in the recruitment missions as well, IIRC.
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"I'm Commander Shepard, and you're standing in the biggest library in Citadel Space. Look me up."