Originally Posted by mimartin
So what do Reapers look like? They are AI too
No they aren't. The squid bodies are merely a vessel for an organic super-collective consciousness. Hence the whole "each a nation" line that Sovereign gives you in ME1 on Virmire. It was hinted at throughout the series and Legion tells you directly in ME2:
It's possible that Karpyshyn or one of the other writers was a fan of Evangelion or Arthur C. Clarke's Childhood's End
(which Anno cited as an inspiration for Evangelion's central plot device that deals with the merged consciousness concept).