"I'm baaaaack. Miss me, Galuf?"
I loved X-Death's, he was such a cliche RPG villain and he did it perfectly bossed up in control, "Fools!!!" being my tribute to him under my user name.
Also because I know he'll get the least votes.
Other than him, Sephiroth. His introduction is a giant katana protruding from the back of the (ex) President of Shinra Inc. The creepy music abruptly stopping once you see the site was...the epitome of what JRPGs are all about, telling a story.