Valka's Bewilderbeast is Valka's Dragon and the King of all Dragons.
This is the Master of the Dragon Den where Valka has lived 20 years ago. Valka literally bows to him as a sign of respect. During the battle of Dragon Sentury Drago's Got a Challenge to Defeat Valka's Bewilderbeast after the Challenge He was Killed by Drago's Bewilderbeast. When Toothless was Free for the Alpha's Command He Went into Toothless's Heart so He can be the Alpha to save all Dragons. In the End of How to Train Your Dragon 2 Toothless can Stay Being as the Alpha.