The Dungeon Master for Friendship is Dragons.
Also known as the Game Master, DM, or GM. This person who shall remain nameless is responsible for the world, characters, and mechanics that the players interact with. This person roleplays NPCs, controls the actions of monsters, and passes judgment on the each player's dice rolls.
This particular DM is more fond of character interaction than the usual "killing monsters and taking their stuff" model of Dungeons and Dragons. Instead of awarding Experience per monster killed and per quest completed, this person chooses to award Experience for campaign objectives and extra feats of achievement - whether they were accomplished through battle or not.
It's not clear why the DM chose to create a campaign setting based on colorful, magical ponies.