A transcript below(thank you Der Kluge of ENWorld):
Conan: You have this image right now, of an action star, tough guy, but there is, for lack of a better term, maybe a slightly nerdy side to Vin Diesel, is that fair to say?
Conan: Please don't rip my head off, reach into my neck, and pull my heart out, but... You can do that later, but.., let's just say a side of you that people might not expect.
Vin: I spent a lot of years playing a game called Dungeons and Dragons.
Vin: Very few people know that I was rolling 20-sided dice and talking like a half-orc
Conan: You would talk in the voice when you played the game?
Vin: Oh, we completely role-played, yea.
Conan: *laughs* you're kidding?!
Vin: (in the voice of a half-orc) "How dare you!?"
Conan: That's amazing! (in a nerdy voice) "Fear not, Gandalf is on the way!"
Conan: That's what I would be, if I was playing with you. You would not let me play with you, probably. You'd be like "that guy's too nerdy, he's gotta go."
Conan: So you played this for like how long?
Vin: For like 24 years.
Conan: For 24 years?! *laughs* I know...
Vin: Now I call it the training ground for imagination.
Conan: Right, well that's very...
Vin: But this was before video games. I started playing in the 70s. And, this was, I mean, I could have played Risk, Monopoly, or D&D.
Conan: Right, which was probably the cooler of those games.
Vin: I think, yea.
Conan: And you created a character for youself, didn't you?
Vin: I created a character... No one knows this, but in Triple-X, one of the tattoos, right above my belly-button, or below my belly button, I don't know why I'm saying this *hoots from audience*, was the name Melkor. And that came from a character that I had, uh..
Conan: That you created in Dungeons and Dragons?
Vin: that I created. That was a Drow witch-hunter. Double-specialized witch-hunter. but this is all
Conan: There are so many nerds watching right now who are just thrilled. Cause you're making them cool, suddenly. All these guys are watching going "Go, Vin Diesel, Go! Go!" All hail, Melkor, you know?
audience: *applause and laughter*
Conan: I think that's neat though. See that you did, see that you'll talk about it.
Notice that while Conan assumes this is all past tense, Diesel talks about playing D&D in the present tense. Very interesting. Sadly, I can't find a direct picture of the tattoo.
After this interview, D&D became a favorite topic in Diesel interviews.
Here he discusses D&D with Jimmy Kimmel:
He says he hasn't "played recently", again he mention's Melkor. He mentions playing as an adult and a player who would get drunk and brandish a gun (which is why I don't allow weapons at the table.) Here's an article also talking about it.
This is Vin Diesel on Shootout:
Very poignant on this one, talks about it lovingly but completely in the past tense. Mentions playing it while being a bouncer. Claims not to know about "now in the age of technology".
Jonathon Ross on the BBC:
This guy from UGO tries to engage Vin Diesel and check his geek chops. Diesel shoots right back and nails the interviewer on his lack of nerd cred.
Here is the coolest interview though:
Vin Diesel is our geek of the week. I'd love to see him in a Drizzt movie. If he's too old to play Drizzt, he'd make a perfect Zaknafarian.