That bio looked really good up until the "made entirely of an almost indestructible metal" part. Really durable would be fine (if you specified limits), but almost indestructible could mean that the character could survive a nuclear explosion and only being dropped into the heart of the sun can hurt him, in which case none of the other characters can touch him. 

In regards to the specifics of his durability, things like how much heat he can withstand, how he reacts to things like EMP's and electrical damage, and his level of resistance to blunt force and piercing attacks are some good bases to cover. Being a robot made of metal, he'd likely be more resistant to blunt force, piercing, and heat damage than he would to EMP and electrical.