Santa Monica has developed all main entries, while Ready at Dawn and Javaground/Sony Online Entertainment-Los Angeles (SOE-LA) developed the three side games. Sony Interactive Entertainment (SIE; formerly Sony Computer Entertainment) has published all games except the mobile phone installment; it was published by Sony Pictures Digital. There are two eras in the God of War series. The first era are the first seven games, which are based on Greek mythology with vengeance as a central motif. God of War (2005), God of War II (2007), and God of War III (2010) comprise its main trilogy; the first two were released on the PS2 with the third on the PlayStation 3 (PS3). The fourth main installment, Ascension (2013), a prequel to the entire series, was also released for the PS3 and features multiplayer. The three side games include Chains of Olympus (2008) and Ghost of Sparta (2010) for the PlayStation Portable (PSP), and Betrayal (2007) for mobile phones that supported the Java Platform, Micro Edition (Java ME). The fifth main installment, also titled God of War (2018), was released for the PlayStation 4 (PS4). It began the second era, which takes the franchise to the world of Norse mythology. To go along with the new installment, Sony released a short prequel story, A Call from the Wilds (2018), as a text-based game through Facebook Messenger.