My favorite commander would have to be Hannibal. The man went behind enemy lines, against a superior enemy for 10 years, gave birth to military strategy as we know it, and even became a pirate to spite Rome after Carthage lost the wars.
As for theorists, I like Tukhachevsky. He invented deep battle, which is currently the best strategy in use by any military today.
Favorite Commander/Military Theorist.
#1"Steal from one and you are a thief. Steal from all and you are the government"