[@SgtEasy] Strangely I always considered Balak to be Shepard's true rival. Sure Shepard fights villains, but they never seem to last more than a single game. Saren, The Collectors, Harbinger. But Balak lasts the entire series.

And the best part is that Balak is not some big evil force to be defeated. He's just a soldier fighting for his people like Shepard. Balak, for me at least, is like the anti-Shepard.

Edit: Even when they meet again in ME:3 "Shepard!" "Balak!"
It was a very "We meet again... FOR THE LAST TIME!!!" moment.