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 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), was also released for the PS3 and serves as a prequel to all other games. 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 second era, which is based on Norse mythology, began with the fifth main installment, also titled God of War (2018), which released for the PlayStation 4 (PS4). 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.