"This is an Imaginary Story... Aren't they all?"
Superman really hit his stride in The Silver Age of Comic Books, which introduced things like multi-colored Kryptonite, Supergirl, Bizarro, and the Fortress of Solitude. Even today, everything the average person knows about Supes (not counting his death) comes from that period.
Then came the Crisis on Infinite Earths, a mega-event that reset the continuity of every DC title. Thus began the modern, John Byrne era of Superman which strove to be more "realistic." Realizing that Silver Age Superman deserved a grand finale, Julius Schwartz hired Alan Moore and Superman ur-artist Curt Swan made the last Silver Age tale--an "imaginary story." Published in September, 1986.
After Superman's life has settled into an easy groove as all the villains lie low, he spends his time helping NASA with experiments. Of course, the villains then go berserk, attacking Metropolis in increasingly grisly ways. Superman takes his friends to the Fortress of Solitude, pursued by the Kryptonite Man, the Legion of Supervillains, and creepiest of all, an enslaved Lex Luthor, mind raped and taken over by the remains of Brainiac.
Superman makes his last stand, and survives by the skin of his teeth. He defeats Brainiac, but realizes there's one last villain: Mxyzptlk. Bored after spending 2,000 years as a mischievous imp, Mxyzptlk has decided to try being truly evil. Superman is no match for Mxyzptlk's godlike power, but thanks to a warning from the Legion of Super-Heroes, he's able to kill Mxyzptlk using the Phantom Zone projector. Appalled that he's violated his code against killing, Superman exposes himself to gold kryptonite (permanently robbing himself of all powers) and apparently commits suicide by exposure to the elements.
Back at the Framing Device, Tim Crane thanks Lois for her story, leaves, passing Lois's husband Jordan Elliot. It's revealed that Jordan Elliot is actually Superman and that he's in his retirement, happy to enjoy an ordinary life for once. Jordan, crazy in love with Lois, winks at the audience, enjoys a Happy Ending... and misses the fact that his infant son is exhibiting Super Strength.
That's the tale. As time went on, the fans rejected the modern era Superman, and the classic Silver Age trappings came back. However, the legacy of this story would continue to endure.
Just as this story was Silver Age Superman's "epilogue" following Crisis on Infinite Earths, a similar story has come in the wake of Final Crisis, Batman's "Whatever Happened to the Caped Crusader??" The two stories are similar in presence, but while "Tomorrow" was a tribute to the Silver Age Superman (whose tenure is debated to last all the way to The Bronze Age of Comic Books; the Golden Age Superman, Kal-L would later return in Infinite Crisis), "Caped Crusader", which followed in the death of Bruce Wayne in Final Crisis, is a tribute/epilogue to all versions of the Bruce Wayne Batman, as told by the various versions of his allies and enemies. Both storylines however, maintain a theme of renewal, "Tomorrow" sees the future of Superman passed onto the next generation, and "Caped Crusader" sees Batman reborn to continue his crusade against injustice.
- Action Girl: Lana. And she does make a difference in the story where even Superman couldn't because the superpowers she gains aren't affected by Kryptonite. Though they can be removed by transmuting the elements in the treatment she took.
- Alien Geometries: Lois described the true form of Mxyzptlk as having "length, width, breadth, and a couple other things."
- Almighty Janitor: In something of a literal sense.
- And I Must Scream: Luthor ...until he musters enough willpower to beg Lana Lang to kill him. She complies.
- Anyone Can Die: Since it was the swan song of the Silver Age Superman, Alan Moore was given a free hand.
- Babies Ever After: At end of the story, Superman lives an ordinary life with Lois and his son Jonathan.
- Berserk Button: You shouldn't have killed Lana, Lightning Lord...
- Big Bad: Mxyzptlk
- Big Bad Wannabe: Brainiac and the League of Supervillains in particular want very much to be Superman's greatest foe, but in the end look rather pathetic (Brainiac ditching Luthor's corpse and desperately trying to reach Superman in the midst of a total system failure, the League running back to the future with their tails between their legs after triggering Supes' Berserk Button).
- Body Horror: The new Brainiac-Luthor team.
- Chekhov's Gun: The trophy the Legion gives Superman.
- The Chessmaster: Mxyzptlk
- Continuity Nod: In Superman/Batman where the World's Finest pair change the grim-and-gritty, dystopian Kingdom Come future into the idyllic Man Of Tomorrow-verse, essentially choosing that alternate future as the "correct" one for DC. If you loved The Silver Age of Comic Books and were irritated by Kingdom Come, it was pretty awesome.
- Creator Cameo: Curt Swan, Jenette Kahn, and Julie Schwartz are all on the cover of Action Comics #583, waving goodbye to Superman.
- Dead Sidekick. Bye, Jimmy Olsen and Krypto.
- Disc One Final Boss: The Luthor/Brainiac fusion.
- Eldritch Abomination: Mr. Mxyzptlk's true form, as well as a...
- Energy Being
Mxyzptlk: You didn't think a 5th-dimensional sorcerer really looked like a funny little man in a bowler hat, did you?
- Eureka Moment: The Legion's gift to Superman, and what the trophy is holding.
- Family-Unfriendly Death: The death of Mr Mxysptlk, who's humanoid Energy Being form is torn in half on panel, as he screams in pain and horror... Also, Lana Lang being fried by electricity from Lightning Lord.
- First Girl Wins: Sadly for Lana, no.
- Lois is both the first girl to appear in the story AND the first girl to appear, period. It's more Unlucky Childhood Friend.
- For the Evulz: Mxyzptlk. Big time.
- Heroic Sacrifice: Many.
- I Cannot Self-Terminate: Luthor gains enough control to beg Lana to kill him to stop Brainiac. She complies.
- I Just Want to Be Normal: Clark, I mean Jordan, got his wish. Jordan mocks Superman in the beginning of the story, proclaiming that the ordinary working Joe is the real hero, then when teased by Lois about really enjoying his life, Jordan remarks that Superman was deluded into thinking the world couldn't go on without him.
- The Ishmael: Lois.
- Locked Out of the Fight: Several of Superman's heroic allies come to help him in the final battle, but are kept out by a Force Field until it's all over.
- Meaningful Rename: Jordan Elliot, the identity adopted by Clark after losing his powers.
- Mercy Kill: Lana gives poor Lex one of these at his pleading.
- Murder the Hypotenuse: Poor Lana. At least it was in an Heroic Sacrifice, but still. . .
- Not-So-Harmless Villain: Everybody, really. Superman is deeply disturbed by this; when the nuisances of the past come back as murderers, what happens when the murderers come back? Special note to Toyman, Prankster, Bizarro, and Mxy.
- Red Eyes, Take Warning
Superman: YOU HURT LANA?!
- Thou Shalt Not Kill: Subverted...and yet, played straight after a fashion:
Superman: I broke my oath. I killed him. Nobody has the right to kill. Not Mxyzptlk... not you... not Superman. Especially not Superman.
- Saturn Queen is shocked that Superman's not bluffing when he attacks the trio with heat vision after their murder of Lana Lang, noting he's prepared to kill.
- Triple Entendre: "This is an Imaginary Story... Aren't they all?", which can be taken several ways:
- This is a What If? story.
- This is a canonical ending to the original Superman tales before John Byrne's reboot.
- All comic books are imaginary stories, so this story is as valid as any other.
- Trickster Archetype: Mxyzptlk remains one. He's just gone from Anansi to (post Face Heel Turn) Loki.
- You Are Too Late: Despite their best efforts, the rest of the worlds heroes are unable to assist Superman in time, as Braniac's force field is blocking off the Fortress, even after his death. Once it falls, its already too late.
- Zeerust: The fashion in the story is less futuristic/modern and more '80s. Lois Lane's dress in particular looks exactly like Bond Girl Lupe Lamora's.