Diablo II is a sequel to Diablo I. Diablo was a graphical sorta real time attempt at a roguelike, of the hack heritage. It was heavily influenced by the Moria and Angband* Roguelikes, and "the" Balrog is the Moria one. So Diablo and LOTR share the same demon inspiration.
Here's a direct quote :
"Having met Blizzard's Allen Adham at CES, Brevik took advantage of the opportunity to plug his own idea for a PC game: "I came up with the idea for Diablo ... when I was high-school," says Brevik. "It was modified over and over until it solidified when I was in college and got hooked on an ASCII game called Moria/Angband. When we pitched Diablo to Blizzard, we pitched a turn-based, single-player DOS game.""
Heh... anyway if you think this all sounds a bit geeky...
you'll find my name on the startup screen for the Roguelike, Angband! If a guy called Sean and I had not picked up Angband again to finish it and release it to the world from Warwick University, it would almost certainly have died, which perhaps would have led to there being no Diablo in computer game history, and a different looking balrog in the Lord of the Rings. So how many degrees of separation does MBTI Geoff have from the Lord of the Rings Balrog