Blade/Slade/Nick Carter/Ness Carter/D-Boy/Takaya Aiba, (those are all his names... there are three different versions of the anime, very confusing) amnesiac guy, shaggy, longish black hair, green eyes, a scar over one of his eyes, can change into a metallic 'superhero', Teknoman.
Star/Aki, a Space Knight, long dark blue hair, dark eyes, sweet and brave girl who falls in love with Blade.
Ringo/Noal, cocky but brave blond guy, Space Knight, childhood friend of Star's, pilot of the space ship Blue Earth, doesn't like Blade in the slightest, at first, but they become friends over time.
Commander Jamison/Chief Freeman, seriously cool albino guy.
Saber/Evil/Cain Carter/Shinya Aiba, Blade's evil twin, looks just like him, but his hair is a lighter shade of green, his skin is much paler, he doesn't have the scar, and his eyes are red. Plus, he's psycho
all the time, Blade only goes berserk once in a while.
Shara/Shara Carter/Miyuki Aiba, Blade's younger sister, white-ish pale green hair, lilac eyes, sweet girl, Blade talks about her the whole time.
Rebin(Levin?)/Maggie, a redhead, crossdressing male in the original Japanese version, tomboyish female in the American and British/Australian one, an engineer and computer genious.
I can go on, if you're still not sure...
There's a second season, by the way, which I haven't seen and know very little about. Characters of the second season include Yumi Francoise, Natasha something, David Krueger, Dead End, and some more.
What are you doing, Dreamer? *pokes*