Many years ago there as a beta of a pvp feature in WoW, you couldn't just click a button, you had to go to Ashenvale to queue up, I want to say it was the first battleground, but I'm not sure. I remember downloading the beta stuff, and I logged in, I think it sent us straight to Ashenvale. At this point I looked around and everyone was named Leeroy or Jenkins or some crazy spelling of it. Within seconds I received a bombardment of guild invites from a plethora of guilds all with a variation on the name.
Alt-Tab was pressed, and google was typed, eyeballs absorbed this.
I'm not sure but I don't think the original was on YouTube. Was there YouTube? I think there was, but I don't think it was the end all be all of video content it is now. Mr. Jenkins became a phenomenon. He became a trading card illustrated by Mike Krahulik of Penny Arcade. There are shirts, and he even made it into Hearthstone. The idea that this video is 10 years old is absolute insanity to me. I feel old, not just old, eld!
The odds of you having not seen this are pretty slim. But its a great throwback and on the anniversary, you should totally watch it. Just have your headphones down low because when he lets loose the LEEEROY JEEEENKIIINS! Its loud, awesome, and perfectly delivered.