My favorite would have to be Groose. It was Ghirahim, but towards the end he got all serious and evil, which I guess fits his title as the Demon Lord, but it just felt to un-Ghirahim. I wished he could have gotten Impa and Groose out of the way in a quirky way instead of just kicking them down. At least he made fun of Groose's hair, though!
Anyway, I loved Groose because you could really see him growing as a person. Before he dove into the Sealed Grounds. He was loud, cocky, and completely ignorant that Link could've been the true hero. But after Link defeats The Imprisoned for the first time, Groose realized that he isn't the true hero, and you can find him pathetically hitting a wall outside the Sealed Temple. But once you revisit the temple, you find that Groose has learned that he too can help, and builds the Groosenator, which helps Link take down the Imprisoned for the second and third time. And [SPOILERS] just before the final Ghirahim fight, when Zelda walks out, and at the end of the game when Impa fades away, we see Groose tearing up in disbelief. This, in my opinion, is expert character development, and made Groose one of the most memorable characters in SS, if the Groose's Theme didn't do that already.
