He's from Sonic the Hedgehog, and he's the red dude who punches things. He has stuff to do with the Chaos Emeralds and stuff.
A better answer: He is the Guardian of the Master Emerald (which is located on 'The Floating Island'). Incredibly strong (strongest of any living character in the series), can glide, uses the bone spikes on his fists to climb walls, and has a direct connection to 'Chaos Energy' (while using this, Shadow calls it 'Chaos Control'). He can run reasonably fast, but when compared to Sonic or Shadow he is slow (a good comparison is the speed difference between an Ocean wave and a stream).