Ruthless

Ruthless was Hakkap One-leg's powerful black storm drake. Together, the two of them were unbeatable in battle.

Trivia

 * Hakkap and Ruthless are references to Hiccup and Toothless from the 2010 animated movie .

Speculation
Ruthless most likely accompanied Hakkap during the great battle inside a thunderstorm that ended with Hakkap's death. If so, Ruthless may have perished alongside his master.