I wasn't talking about the appearance =P
Casshern (original) = Teenage boy that willingly transformed into a battle robot to fight evil.
Rock = Assistant robot that willingly upgraded into a battle robot to fight evil.
Quickman = Casshern recolor but without the C in his chest.
Friender = Dog transformed into robot to help Casshern (it was also done to save his live though). He can turn into an actual jet, a car, a drill, and a submarine.
Rush = Robot dog created to help Rockman. He can turn into a "jet," a drill, a car, a submarine, and a battle armor.
Also just because...
Buraiking Boss = Robot that somehow obtained a concience and then formed an army of robots to rebel against the humans. He's also bald.
Sigma = Robot that turned maverick and the formed an army of mavericks to rebel against the humans. He's bald too.
Casshern = Neo human (or cyborg if you want) that fights against an army of robots that want to destroy humans in a futuristic/post-apocalyptic world.
X = Reploid that fights against an army of robots that want to destroy humans in a futuristic/post-apocalyptic world.