Short answers, pulled from the story.
Dragon Slayer is a video game franchise created by Nihon Falcom and designed by Yoshio Kiya. The series began in 1984 and is historically significant as the progenitor of the action role-playing game genre and a founder of the Japanese role-playing game industry.
The first Dragon Slayer game was released in 1984 for the NEC PC-8801. It was later ported to the MSX by Square, making it one of the first titles that company ever published.
Dragon Slayer II: Xanadu sold more than 400,000 copies in Japan, setting sales records for PC games in the country at the time of its 1985 release.
Dragon Slayer and its sequel Xanadu are credited with influencing The Legend of Zelda, Hydlide, and Falcom's own Ys series. According to GamesTM and journalist John Szczepaniak, Enix's Dragon Quest was also influenced by Dragon Slayer.
Yuzo Koshiro composed the soundtrack for Xanadu Scenario II in 1986, which was his first video game music soundtrack. The Falcom Sound Team JDK also contributed music across the broader Dragon Slayer series.
Dragon Slayer IV: Drasle Family reached North American NES shelves as Legacy of the Wizard, and Faxanadu also released on the NES in North America. An English version of Sorcerian was published by Sierra On-Line for MS-DOS in 1990, and The Legend of Heroes appeared on TurboGrafx-CD in 1991.