Ripperclaw

"An aristocrat never growls. You must be one of those mongrel Nightmares. We pure greenbloods descended from the great Ripperclaw himself would never dream of doing anything so common."

- Fireworm to Killer in Book 1

Ripperclaw is a historical dragon figure mentioned in How to Train Your Dragon.

Physical Appearance
No specific description is given of Ripperclaw, but he presumably looks like a typical Monstrous Nightmare dragon.

How to Train Your Dragon
Fireworm mentions Ripperclaw as an ancestral aristocratic Monstrous Nightmare. It is meant to be a slight to a rival Monstrous Nightmare, Killer. Her statement indicates there may be division amongst the species of those considered aristocratic and those considered mongrels or common.