Part re-imagining, part Adaptation Distillation, the Ultimate line was originally an attempt by Marvel Comics to tempt readers into comics without being scared off by the decades of Back Story and Retcons in the official universe. The line was launched in November 2000 with the release of the first issue of Ultimate Spider-Man. This had already been attempted by various other experiments - the Marvel Comics 2 comic line, The New Universe, Heroes Reborn, etc., but none of those met with the success the Ultimate Marvel line did, except for Spider-Girl (the original MC2 title, and via multiple relaunches the only survivor of the line), which became the longest running Spidey spin-off ever.As basically an experiment which does not affect the main universe, changes and revelations are more permanent, and the universe as a whole has plot lines and continuity more neatly intertwined; notably, the connections to the Weapon X project from Ultimate X-Men and the history of the Super-SoldierSerum/Captain America from The Ultimates. As the line has grown and accumulated its own continuity, its focus has shifted from distilling old stories to making all kinds of sweeping changes, like killing X-Men's sacred cows or replacing Peter Parker as Spider-Man.The Ultimate Marvel universe is part of Marvel's multiverse, specifically Earth-1610, while the main Marvel Earth is Earth-616 (though former EIC Joe Quesada despises the designation). Marvel has insisted doing a crossover between the two would be a lame and tired idea. At one point, it seemed that Ultimate Fantastic Four would have such a crossover, but it turned out to be a trick by denizens of a strange Alternate Universe: the one of the Marvel Zombies in their debut appearance. A true crossover was released in 2012, teaming up the mainstream and Ultimate Spider-Men for the franchise's 50th anniversary, though with Ultimate Peter Parker dead and his mantle now worn by Miles Morales the circumstances are very different than when the original statement was made. A new crossover named Hunger featured Earth-616's Galactus being transported to the Ultimate Universe as a result of Age of Ultron, upon his arrival, he found himself merged with his Ultimate counterpart, Gah Lak Tus, creating a being with a greater hunger than before. This is dealt with in Cataclysm: The Ultimates' Last Stand, a title in which the newly merged Galactus arrives on Earth. More recently, the time-displaced O5 X-Men and X-23 cross-over with the Ultimate Universe in an arc beginning with Issue 31 of their book.Major series in the Ultimate Marvel Universe are:
The Ultimates: The only one that's not just a remake of its classic version, it re-imagines The Avengers as a metahuman strike force under S.H.I.E.L.D.. Was published as three miniseries rather than a single ongoing title.
All-New Ultimates: No relation to the previous SHIELD-sponsored team; this is a group of the Ultimate U's teen heroes; Miles Morales' Spider-Man, Spider-Woman (now going by Black Widow), Bombshell, Kitty Pryde, Cloak, and Dagger.
Note that technically, the titles of vol. 2 and 3 have been renamed from "Ultimate _____" to "Ultimate Comics: _____"; we're just sticking with the original format here for convenience (face it, titles like "Ultimate Comics: New Ultimates" are redundant and kind of a mouthful).
Miniseries and Events
Ultimate Marvel Team-Up, a series where Spider-Man teamed up with various Ultimate heroes; it was more episodic and light than the main Ultimate Spider-Man series. At least partly Canon Discontinuity, some elements are referenced by later series but other elements are contradicted.
Ultimate Daredevil and Elektra and Ultimate Elektra: Devil's Due.
Ultimate Adventures, an odd book about a Batman parody that lost a competition to get upgraded to an ongoing. Not officially Canon Discontinuity, but don't expect anyone to mention it outside of Official Handbooks to Ultimate Marvel. It was part of the infamous "U-Decide" event which also involved Peter David's Captain Marvel and Bill Jemas' Marville.
Ultimate War, an X-Men/Ultimates crossover. Magneto shows up after being thought dead, thanks to the fact that Xavier mindwiped him instead of killing him. The government ain't happy, and they send out the Ultimates.
Ultimate Six, a Spider-Man/Ultimates crossover. Spidey's Rogues Gallery escapes imprisonment (forming an Ultimate take on the Sinister Six) and they go after him with the Ultimates in pursuit.
The Ultimate Galactus trilogy, consisting of Ultimate Nightmare, Ultimate Secret, and Ultimate Extinction. As you might guess from its name, the Eater of Worlds is headed towards Earth and the Ultimates, X-Men and Fantastic Four have to band together to drive it off.
Ultimate Vision, a miniseries spun off from Ultimate Galactus.
Ultimate X4, an X-Men/Fantastic Four crossover. Someone steals Cerebro from the X-Men and frames the Four for it.
Ultimate Iron Man, two miniseries detailing the character's origin. Canon Discontinuity thanks to Mark Millar, who later established that this was a fictional in-universe TV show so that he could go in other directions with Tony's past.
Ultimate Power, a crossover between Ultimate Marvel and Supreme Power.
Ultimate Wolverine vs. Hulk, Nick Fury sends Wolverine to kill the Hulk. Hijinks ensue.
Ultimate Human, billed as Iron Man versus the Hulk, and derailed somewhat by the appearance of the Ultimate Leader.
Ultimate Origins, which expands on the Meta Origin and the connections between various forces and mysteries in Ultimate Marvel.
Ultimatum: Requiem specials (Spider-Man: Requiem, Fantastic Four: Requiem, and X-Men: Requiem), ending their respective series before the Ultimate Comics reboot.
Ultimate Armor Wars, an adaptation of the classic Iron Man story, it features Tony Stark trying to recover an item and discovers that someone's stolen his Iron Man tech and sold it to various criminals that now employ it.
The Ultimate Doomsday trilogy, a Spider-Man/Fantastic Four crossover consisting of Ultimate Enemy, Ultimate Mystery, and Ultimate Doom. Superhumans and scientific installations have been targeted by a new mystery Big Bad.
Ultimate Thor, the origin story of the god of Thunder.
Ultimate Fallout: Spider-Man No More: As the world mourns Peter Parker, the superhero community starts considering and planning for the future...
Ultimate Hawkeye: Tying in to The Ultimates; Nick Fury sends Hawkeye, the Hulk, Karen Grant, Firestar and Guardian to investigate and retrieve a super-powering 'Serum' developed by the S.E.A.R. (South-East Asian Republic) military.
Divided We Fall and United We Stand: A crossover affecting all the Ultimate Comics titles, the story involves a divided United States after Washington D.C. is annihilated and Sentinels begin to run rampant in the southwestern states. As a result, the entire nation is divided into smaller divisions as America is on the brink of collapsing. The second half of the story is covered in United We Stand, where Captain America returns from self-imposed exile and is subsequently voted in as the President of the United States.
Anyone Can Die: Unlike the mainstream universe, it's permanent. Notable examples include Ultimatum and Death of Spider Man
Big Bad: Before "Ultimatum", Magneto was the closest contender for this title, being a threat to both the X-Men and the Ultimates, and one of S.H.I.E.L.D.'s highest priority target.
Big Good: There isn't one. No-one's noble enough, or sane enough. Not even Captain America.
Breaking the Fellowship: Happened to the X-Men and Fantastic Four in Ultimatum due to the losses each suffered in that event. The remaining X-Men eventually regrouped, especially after Spider-Man died, but the Four were cemented as broken up forever when Reed turned evil as a Knight Templar.
Clueless Mystery: The Ultimate Enemy trilogy. Spider-Man, the Baxter Building, Nick Fury, and a few others are attacked by aliens or strange tentacle monsters. No clues or hints are given, and there's no foreshadowing of any kind as to who might be behind this, until the end of the second half of the story, where it's revealed to be Reed Richards.
Comic Book Death: Averted; when you die in this universe, you die (with very few exceptions)
The exceptions are Norman Osborne (it is hinted that this may actually be his super power), Gwen Stacey (one could argue that she was never killed just predisposed), Psylocke (as a telepath, she can transport her consciousness into multiple hosts), and Tony Stark (same deal as Psylocke, but could implant his consciousness into advanced technology. He then used the Infinity Gems to revive his body and implant his consciousness back in it).
Continuity Snarl: There are at least three different versions of Bolivar Trask, none of whom have anything in common with one another. One of them is a government funded scientist, and the creator of the Sentinels. Another is a corporate big-shot, with almost no actual operational knowledge of science, who is partially responsible for the origin of Venom, and the third is a scientist hired by the Fenris Twins to build Sentinels, before dying in an explosion.
Crapsack World: Amazingly, the Ultimate Marvel Universe is even more of one than the mainstream universe; as noted above, it has a Darker and Edgier approach, and, unlike the mainstream, you can't rely on cosmic schemes to come back to life after suffering a horrible death. With the exception of Thor...
It's so bad that Galactus himself declares this universe is broken.
Deconstruction: You could argue this is a deconstruction of the regular Marvel Universe. Many storylines use this as a basis.
Genetic Engineering is the New Nuke: Stated as such by Nick Fury at the end of Ultimate Six. Outside of the Asgardians, just about every existing superhuman can be traced back to military experiments in some way. Yes, including the mutants.
Humans Are Special: Nick Fury phrases it differently, but the point is the same. Humans can kick the crap out of anything.
Meta Origin: The Ultimate line simplifies many random elements by having many of the world's superheroes connected to Captain America's Super Serum in some form or another. The Hulk was accidentally created while Dr. Banner was trying to recreate the serum, Norman Osborn accidentally created Spider-Man while attempting the same thing, Weapon X and the entire mutant race were created as the Canadian response to the Serum, and so on.
There are a lot of other examples. The Wasp was Asian-American, Ben Reilly and the most recent Vision are black, Hurricane was North Korean, Crimson Dynamo and the Abomination were Chinese, Abigail Brand are Ambiguously Brown.
Revisiting The Roots: From time to time, an element that was changed for the adaption, suddenly tilts back to the way it was (or is) in the regular Marvel Universe. For example, the Avengers began as a group of super-powered agents of SHIELD, and stayed that way for the first two arcs... and at the end of the second, they are a group of super heroes working on their own, financed by the wealth of Tony Stark (precisely their usual status in the Marvel Universe, at least before the contemporary Civil War). The Scarlet Witch donned her classic suit, Thor is shown to actually be a god from Asgard and not just a lunatic, and some topics that were initially avoided for being too fantastic (such as aliens and time-travel) finally got their space.
Took a Level in Jerkass: Several characters, most notably the Ultimates (this universe's version of the Avengers), Wolverine, and most notably Ant-Man, are much more cynical and anti-heroic than their mainstream counterpart.