Scratch is a Grey & Black furred hedghog with a scar across his eye. He is half android so when he gets angry, his eyes turn bright red.
He is a jerk to almost everyone around him including Silver, his rival who he hates because they both have telekinesis powers. He started out on Eggmans side after being turned into a cyborg but he changed onto the good side after learning from past mistakes and putting Eggmans plot to use him as a weapon to take over the world as completely ineffective which made him switch sides, as well as his new replacement. He happens to be a rebel.
In his sonic adventure 3 story he tells when he was 1 he and his family were killed in an attack on their tribe but eggman found what was left of their tribe and turned scratch into a android. As he grew up the attempt to turn him into a weapon to take over the Earth but it failed and so eggman made a new version causing Scratch to leave.