Notable for its green hue, this flammable liquid finds its roots in the Alchemists' Guild, an ancient society of learned men based in King's Landing. When ignited, Wildfire burns so hot that only sand can extinguish it.
In the second season, Wildfire played a major role at the Battle of the Blackwater during the War of the Five Kings. It showed up again (in a major way) in season six, when it killed . . . everyone? We can only cross our fingers that this unpredictable weapon will make a return in the final season.