Everyday thug Archibald Dyker got himself mutated by a diamond-powered laser back in the 70s, when that kind of thing happened a lot. After that he was still a thug, but one with diamond-hard skin.
He was a little more glam back in the day but he has remained the same unlovable lunkhead for fifty years.
References: [wikipedia.org: Diamondhead (comics)]
[writeups.org: Diamondhead]
[crystal]