Coloklurt was a dragon living during the Age of Fire. He was a wild dragon that lived in the east and was notorious for being one of the few to willingly join the Dragon-riders in search for revenge over his enemies (possibly elves).
When he reached the Isle of Ice, he was in poor state, but then turned into one of the sleekest fighters, raiding the elven coast.
Being part of the fighting stock means he had lost a trial and was castrated.