playerbase remained active, and the modders claimed its popularity hastened Microsoft's plans to release a Windows version of Halo: The Master Chief Collection. Other appearances Halo characters have appeared in tie-ins, such as the characters Spartan Nicole-458 and the Arbiter being playable fighters in Dead or Alive 4 and Killer Instinct: Season Three, respectively. Master Chief was added as a playable character in Fortnite alongside a stage inspired by a Halo multiplayer map in 2020. Another game, Halo 2600, has the players control Master Chief and fight through four regions filled with enemies. It was written by Ed Fries, former vice president of game publishing at Microsoft, in 2010 for the Atari 2600. The Halo theme tune was also available as downloadable content for Guitar Hero III: Legends of Rock. In Forza Horizon 4 one level has the player racing across the map in the Warthog as the Master Chief, with the Halo ring visible in the sky, Cortana on the radio and various Covenant based obstacles to avoid. Cultural influences and themes In 2006, in acknowledgment of the "wealth of influences adopted by the Bungie team", a list of Bungie employees' favorite science fiction material was published on the company's website. The developers acknowledged that the Halo series' use of ring-shaped megastructures followed on from concepts featured in Larry Niven's Ringworld and Iain M. Banks' Culture series (of which Consider Phlebas and Excession were said to be particularly influential). In a retrospective article in Edge, Bungie's Jaime Griesemer commented, "The influence of something like Ringworld isn't necessarily in the design – it's in that feeling of being somewhere else. That sense of scale and an epic story going on out there." Griesemer also explained, "One of the main sources of inspiration was Armor [by John Steakley], in which a soldier has to constantly re-live the same war over and over again. That sense of hopelessness, a relentless battle, was influential." The Flood were influenced by the assimilating alien species in Christopher Rowley's The Vang; it has also been speculated that the Master Chief's name "John 117" may have been a reference to a character named Jon 6725416 in Rowley's Starhammer, or to the John Spartan character of Demolition Man. An IGN article exploring the literary influences present in the Halo franchise commented on similarities between Halo and Orson Scott Card's Ender's Game: aspects of the SPARTAN Project and the