Jeff Anderson is not a nerd. The 40-year-old chief executive of Westwood (Mass.) video game developer Turbine is six feet tall, with the frame of an NFL linebacker. Nevertheless, he presides over a vast and rapidly growing virtual world of elves, orcs, dragons, and hobbits. In April, Anderson’s company took the wraps off the Lord of the Rings Online, a massively multiplayer online role-playing game (MMORPG) for PC, based on J.R.R. Tolkien’s classic books. The explosive growth of the game—players have created some 4 million unique characters in just five months—has vaulted the company into the top tier of online game design companies and made it the largest privately held developer of massively multiplayer games in the U.S.