Wasn't there a thread for this already?
Alexander (Lord Knight) - I roleplayed a character named Alexander before. And it became my first RO name to use- consequently. Although Alexander was originally for a long long long....long time until this server- a Sin X. But yeah.
Hayate (Assassin Cross) - Once upon a time, like 10 years ago, there was something called the Sega Saturn. And it came out with an amazing game that no one has ever heard of. Dragon Force. It was a strategy game of sorts. In the game, there was a secret / hidden character named Hayate, who is widely and well-foundedly believed to be the best Ninja in the game. Ninjas become assassins at some point anyway for the title. So close enough.
Arion (High Wizard) - Random name generator. At some point, someone in the FF series was named Arion apparently. I've given that name to my mages ever since.
Shinobu (Creator) - From the Love Hina anime / manga series. Shinobu was the youngest of the girls in the house; the shy, sensitive, innocent and cute one. Personally, if I was the main character- I would have opted to uh-....well, I'll tell you when you're older. Shinobu ftw about explains it.
Tristan (Stalker) - Random. No seriously. Just a name, with actually no backing to it. I never intended for it to be a serious character, just a gank rogue card hunter. And then a year later...
Leon (Monk) - Also from the Dragon Force series. He was the leader of Topaz nation, and was also, a monk! As far as monks went, he was the pwnage one.
Gades (Crusader) - Once upon a time, before Sega Saturn, AND Dragon Force, was the Super Nintendo. One of the best RPGs of all time was made for the Super Nintendo. Lufia. Gades was one the four sinistrals (which were more or less evil gods). The God of destruction, and the juggernaut of the 4. Seemed fitting.
Tara (Priestess) - Also, from a roleplay. Although this one was a character someone else roleplayed. /shrug
I'm sure I'm missing a few, but I think I covered the more well-known ones anyway. And some of them, you don't need to know anyway.