There has been one constant in MMOs for the last eight years. There have been casual MMOs, raiding MMOs, MMOs in space and MMOs in the future but, through them all, the Holy Trinity has been a constant. The concept of the tank, the healer and the DPS has been ingrained in our heads over years of constant use. When we face a boss, be it with four of our friends or nineteen of them, it has almost always been with a tank leading the way, a healer healing him and DPS killing the boss. Sure, there have been a few exceptions, the Shade of Aran from Karazhan being a notable exception, but the exceptions have been few and far between. The Trinity has always been there.