2001 Commander Keen received mixed reviews from critics. The graphics were both praised and criticized; reviewers praised the art style and the "bright and colorful" graphics, but disparaged the "busy" backgrounds and lackluster animations as making the game feel "choppy", and complained that the graphical updates did not reflect the ten years since the last releases. The gameplay similarly received mixed opinions; reviewers were split between praising the difficult, "old school" gameplay as a successful adaptation of the originals and dismissing the "aging" gameplay as sound but not comparing well to more recent games. Reviewers concluded that the game was an "acquired taste" best suited for fans of the original series or younger players. Legacy Ideas from the Deep's first royalty check from Apogee in January 1991 convinced them that they no longer needed their day jobs at Softdisk but could devote themselves full-time to their own ideas, leading to the founding of id Software in February. In the summer of 1991, id hosted a seminar for game developers with the intention of licensing the Commander Keen engine; they did so, forming the spiritual predecessor to both QuakeCon and id's standard of licensing their game engines. One of the enemies created for "Secret of the Oracle", the Dopefish, has since the game's release become one of the video game industry's biggest in-jokes, making cameo appearances in other games. The Dopefish, which Hall describes as "just a stupid green fish", is described in "Secret of the Oracle" as "the second-dumbest creature in the universe". It has appeared in dozens of other games since its initial appearance, as references, images, or the phrase "Dopefish Lives". The Standard Galactic Alphabet, a writing system used to depict alien languages in the galaxy throughout the series, is used for textual signs and directions and was created by Tom Hall beginning with Invasion of the Vorticons as a way to pass hidden messages to players. It is a substitution cypher to the Latin alphabet, including the letters A-Z, opening and closing quotation marks, and a full stop. In 2019, it was added to the Under-ConScript Unicode Registry, using the codepoints to , and is included in the GNU Unifont CSUR extension. The Standard Galactic Alphabet also appears in the game Minecraft as the script and symbols used for its Enchanting Table. In January 2018, John Romero and Tom Hall stated on Twitter that Billy Blaze is