The Rat King is a quest with an eponymous boss. Defeating this boss will unlock the Rat Quest Pet. The quest scroll can be purchased from the Quest shop for 4 gems. The Rat King's HP (1200) makes this a long quest and its strength multiplier (2.5) makes this a hard quest. Without using Warrior or Mage boss damaging skills, a four-person party can typically finish this quest in about four weeks. The high difficulty means missed Dailies will cause much damage to the group; having a Healer in the party is highly recommended.