I-R0k is what you would call a griefer, also known as… a lot of words we don't feel comfortable printing here. Basically, they're the jerks of the Internet. I-R0k only appears twice in the book, but it's all because of him, and his failed blackmail attempt against Aech and Parzival that the Sixers find the Copper Key sooner than they ever would have on their own.
As if his avatar name weren't enough of a clue that he's a great big buttface, he's also the type of guy that, when losing an argument he started, says things like, "If I didn't spend so much time offline, getting laid I'd probably know just as much worthless shit as you two do" (3.85). Oh, I-R0k, we think U-5uk. If there were an achievement for lamest antagonist ever, you'd win.