Creator Breakdown: Morrison's father died during the writing of this book, which probably led to the scenes where Clark Kent had to deal with Jonathan Kent's death as well as the talk with Jor-El in the afterlife.
Inspiration for the Work: Morrison and Quitely both cite a Superman cosplayer they encountered at a convention as their primary inspiration for how to portray the character, noting his laid-back posture and attitude that denoted a man who couldn't be harmed by anything.
Recycled Script: A few moments in this series will seem pretty familiar if you read Morrison's New X-Men. There's a poignant scene involving a spaceship hurtling into the sun, a particularly nasty bald supervillain who eventually gets reeducated by the heroes, a forward-thinking academic who wants to lead human society into a new era, and a story about a future generation of heroes who use Time Travel to stop a villain from conquering Earth. Most noticeably: the series ends with the death of a Messianic Archetype thematically associated with the sun, with that character eventually transcending time and space and traveling back in time to comfort one of the main characters at the grave of a loved one.
When asked about the book's continuity with All-Star Batman And Robin, Morrison is vague and indifferent about it. The timeline, with Batman being near the start of the character's crimefighting career and Superman being about the end of his life, made it plausible according to them.
On the subject of the Unknown Superman's existence beyond a disguise Clark used to visit Pa Kent in the past, Morrison simply said they liked to think there was such a character in some "dark century" but still never outright gave a definite answer.
There was consideration by Morrison of doing a trio of two-issue spinoffs expanding the world before deciding to leave All-Star as a singular work:
Superman vs. Satan!, about a younger pre-flight Superman in his first year in Metropolis, which eventually became the basis of Morrison's Action Comics run.
Son of Superman, about the test-tube child of Lois and Clark hinted at in the book's final pages, and his team-up with Batman's son inspired by the original 1970s Super Sons stories; ideas from this later folded into the chapter The Just in The Multiversity.
Men of Tomorrow, a "huge, generational Superman Squad cosmic epic".
Word of God: Morrison confirmed that Jimmy Olsen knows that Clark Kent is Superman, but kept hush hush about it out of respect and acknowledgment that there's likely a very good reason for the Secret Identity.
