Dozens of Square Enix companion books have been produced since 1998, when video game developer Square began to produce books that focused on artwork, developer interviews, and background information on the fictional worlds and characters in its games rather than on gameplay details. The first series of these books was the Perfect Works series, written and published by Square subsidiary DigiCube. They produced three books between 1998 and 1999 before the line was stopped in favor of the Ultimania series. This series of books is written by Studio BentStuff, which had previously written game guides for Square for Final Fantasy VII. They were published by DigiCube until the company was dissolved in 2003. Square merged with video game publisher Enix on April 1, 2003 to form Square Enix, which resumed publication of the companion books. Sometimes, multiple books have been written per game or revised editions have been published years afterwards. One of the books, Final Fantasy IX Ultimania Online, was solely published online as part of an experiment by Square Enix with online content delivery. The Ultimania series had sold over 10 million books by July 2007. (Full list...)