Entity Cyborg (current progress 14/02/2014 is: 90%)
he will defend you against other mobs.
he has some inventory.
He will get items from the floor for you.
He follow you, but not as the dog does. He try to stay 5 blocks away from you, so you can mine without interferences of him.
You need to recharge his battery with the sun.
He has JetPack!
He is very strong!