Alargan is a dragon referred to the "Dragon Lord". It works for Lord Rendtail.
Alargan can hit really hard and can even 1-hit the toughest of warriors. The best chance of winning against him is being a Rogue or Sorcerer.
The best tactic is by running around the boss chamber and shooting him and using skills. Kelvin is also one of the best pets for him as the AA can stun him.