Where did the Jem'Hadar come from?

I was given information that this was a genetically engineered race of people that had very tough skin, and they could just fight and not get hurt. What has tough skin? An elephant has tough skin, a rhinoceros has tough skin. So I based the skin - basically the rolls and everything like that on rhinoceros skin, and I used a dinosaur plate on the top of the head. The horn then [came] from the rhinoceros.