Short answers, pulled from the story.
Yuji Horii created the Dragon Quest video game franchise after winning a 1982 programming contest sponsored by Enix. Koichi Nakamura and Yukinobu Chida joined Horii to release The Portopia Serial Murder Case before forming the team that developed Dragon Quest.
The first Dragon Quest game was released in Japan on the 27th of May 1986 following its development by Enix. The Japanese release of every subsequent Dragon Quest title continued on a Saturday until Dragon Quest X which came out on Thursday the 2nd of August 2012.
The first six Dragon Quest stories were released under the title Dragon Warrior in North America to avoid trademark conflict with a pen-and-paper role-playing game published by Simulations Publications. Square Enix registered the Dragon Quest trademark in the United States on the 23rd of July 2002 allowing later titles like Dragon Quest VIII: Journey of the Cursed King to use the original name.
A small blue blob shaped like a water droplet with large round black eyes became the official mascot of the series and appeared in every Dragon Quest game. Series designer Yuji Horii cited this creature as an example of Toriyama's artistic power and it usually serves as one of the first monsters players encounter.
An augmented reality game called Dragon Quest Walk was released for Android and iOS mobile phones in September 2019. This release followed other spin-off titles including Dragon Quest Builders which came out in 2016 with a sequel arriving on the 12th of July 2019 for Switch and PS4.