Probably Viral from Gurren Lagann. His theme is great and it fits him perfectly.

[youtube]k2gopjn5RW0[/youtube]

I have a bunch of others that I like a lot though, so I'll just list and link them.

[url=https://www.youtube.com/watch?v=gAPGBBo6p_o]Kira's theme[/url] from Death Note, which was essentially the "shit's going down" music for Kira stuff.

[url=https://www.youtube.com/watch?v=Cl84Uf4EgAQ]Zero's theme[/url] from Code Geass, which played whenever Lelouch/Zero was pulling off some of his crazy shenanigans.

[url=https://www.youtube.com/watch?v=vWZs5POCp0I]Raygou's theme[/url] from Kill la Kill

[url=https://www.youtube.com/watch?v=JbXVNKtmWnc]Kefka's final boss music[/url] from Final Fantasy III/VI (stupid international numbering confusion) is a mix of all of his various theme songs throughout the game and is pretty awesome.

[url=https://www.youtube.com/watch?v=9toMoL8fW-4]Ridley's theme[/url] from Super Metroid is neat, I've got tons of nostalgia attached to it.

[url=https://www.youtube.com/watch?v=Yigc4z1gFA4]Frog's theme[/url] from Chrono Trigger is great and another one that is nostalgia-laden for me, and all the other character themes from Chrono Trigger are also great, so that's a plus.

Although it's a boss theme and only shows up the one time you face it, the [url=https://www.youtube.com/watch?v=DzWFWCH_lTE]Taurus Demon theme[/url] from Dark Souls is great and gets me hyped the fuck up whenever I hear it.

[url=https://www.youtube.com/watch?v=vU8eL2CjzHw]The Rains of Castamere[/url] is kind of the Lannister family theme in Game of Thrones, rather than being for a specific character, but it's good so I'm listing it anyway.

And I think that's enough of me being an asshole and linking every character theme I could think of that I liked. :hehe