Leeroy Jenkins is a WoW chara that appeared in one youtube video, and it was a joke about raiding parties that calculate so much percentages of their raid-survivability, apparently the user who was playing the chara went to grab a snack while the rest of the gang was numbercruching, when he returned, he simply yelled "alright let's do this! LEEEEROOOOY JEEEENKINS!" and charged in to the 'wasp nest' so to say XD causing a total wipe. everyone blamed him at the end, but in the end he was, 'at least i have chicken' xD
so yeah, it's not certain if that chara/user are actual or if it all was acting, but yeah.. we got him now as someone who foolishly charges forward x3