Mission began as a role-playing game in my home-brew universe. Initially I played one-offs and inevitably I used the form of words “I have a mission for you…” and this became a shortcut way of referring to the Mission universe.
At the time of writing Mission has been around for 15 years, played on and off until two years ago when I found an enthusiastic group of players at the club I go to, and they got on board for a campaign. I was able to bring in many of the characters and themes that have been in the over-arching story, and we had a jolly time doing that!
In the Mission universe the society is called The Conglomerate, a ragtag bunch of species who more or less rub along together quite well. Human Beings are the ones who interfere with things, set up trade deals, police the Galaxy; at least for those that are interested. The rest party on, or research, or party.
The first book, Hal, a Diaspora, deals with the history of humanity, and how humanity was spread among the stars. it was written in response to the urging of the player group, initially, and then as the idea came together, in response to the wider urgings of those who have played previously.