First off, the order presented here is in no way official; it’s only an attempt to get an overview of all the characters involved in this huge crossover. The terms “main“, “secondary“ and “third-tier characters“ are not meant to describe these characters‘ general importance or their power levels; it’s just a classification of relevance in regards to the Onslaught Crossover. The criteria used to decide who would be counted in which group is listed below. And please remember, even if you don’t personally agree with a specific character’s placement, there’s no real harm done as they are all mentioned on this page.
Listed here are all characters who went face to face with Onslaught during the actual crossover, meaning they appeared in at least one issue from Onslaught: X-Men to Onslaught: Marvel Universe, which besides the two One-shots are all the issues labeled Phase or Impact. That would be all the heroes who fought Onslaught, the characters kidnapped and exploited by him, the villains employed by the entity and Onslaught himself.
The X-Men were the first to learn the true identity of Onslaught when Professor Charles Xavier transformed into him right before their eyes. At the time, the team’s line-up included Storm, Gambit, Iceman, Bishop, Cyclops, Phoenix IV, Wolverine and Cannonball II. During the crossover, Rogue rejoined the team, bringing along Joseph whom she had met earlier.
The Fantastic Four were drawn into the conflict because of Onslaught’s interest in young Franklin Richards, the son of Mr. Fantastic and the Invisible Woman. The foursome are more a family than a superhero team, the other two members being the Invisible Woman’s brother, the Human Torch II, and Mr. Fantastic’s best friend, the Thing. The Torch’s ex-wife, Lyja, bravely tried to help by taking Franklin’s place, but Onslaught saw through the shapeshifter’s deception with the same ease that he cracked the battle armor of Nathaniel Richards, the boy’s grandfather.
Another person with near infinite power that Onslaught wanted to get into his clutches was X-Man. Having had unfortunate experiences of the X-Men, or more specifically Professor Xavier, he instead asked the Avengers for help when he learned of Onslaught. Although having one of the most powerful rosters ever, the team was still shaken from another crisis, the so-called Crossing. Iron Man had become a murder under a villain’s influence, and was replaced with a teenage version of himself. Hawkeye had just returned from a leave of absence to mourn the death of his wife, only to find his ex-girlfriend, the Black Widow, among the team. Giant-Man was helping the Wasp to cope with her transformation into an insectoid hybrid. The Scarlet Witch, back in the fold after the disbanding of Force Works, was unsure how to handle working alongside her estranged husband, the Vision II, whereas Quicksilver and Crystal had decided to give their marriage another try. Not even Thor and Captain America were without problems. The one had to deal with losing his godhood and the entire population of Asgard having vanished; the other had only recently returned to America after having been branded a traitor and kicked out of the US for treason.
Former teammates helped out the Assemblers during the Onslaught crossover. Besides, Captain America’s close friend, the Falcon, there was also the Black Panther and Namor, the Submariner, both of whom had equally strong ties to the Fantastic Four as well.
Cable was actually the one person to correctly guess Onslaught’s true identity without witnessing Xavier’s transformation first hand. However, this knowledge didn’t help much when the entity manipulated the Hulk, aka Dr. Bruce Banner, into going after him. Other lackeys of Onslaught included the partially techno-organic Post, two survivors of the Age of Apocalypse in the forms of Holocaust and the Dark Beast, plus some of McCoy’s pet projects such as Fatale and Havok.
Naturally, a conflict with such dire consequences would call other villains out in the open. Whereas Apocalypse and Dr. Doom both realized that Onslaught was a danger to them as well and therefore helped the heroes to fight the evil entity, Mr. Sinister tried to use the overall confusion to his own advantage, albeit with little success.
Underlined are all those characters who sacrificed themselves in the final battle against Onslaught and were taken to the Heroes Reborn Universe. Only these eighteen characters were clearly shown to be entering Onslaught’s energy form.
There seems to be some confusion wether other heroes entered the entity as well, especially regarding She-Hulk and the Royal Family of the Inhumans. All of them were shown among the people traveling back to the main Marvel Universe in Heroes Return #4. However, in a flashback story in Avengers Annual '99, She-Hulk was clearly established as not among the lost heroes, and when Crystal visited Attilan in Quicksilver #4, there was no mention of the other Inhumans having been considered dead too.
A possible explanation might be that while in the Heroes Reborn universe, the heroes had no clear idea who was actually from the other universe and who not, and that they merely thought they had to bring She-Hulk and the Inhumans along. However, as soon as they breached the dimensional barrier, these Franklin-created duplicates vanished.
In this category are listed all those characters who either personally met Onslaught before the actual crossover, or appeared during the crossover and were directly affected by Onslaught’s actions, like fighting his lackeys, helping to provide the means to defeat him or aiding the major heroes in some other ways.
Moira MacTaggert is the first to be mentioned here. If not for her accessing the Xavier Protocols, leading to the design of the psi-armors, the heroes wouldn’t have been able to even get close to Onslaught. Former X-Men Archangel and Psylocke were part of the group that visited Moira on Muir Island and delivered the armors’ blueprints to New York. Afterwards they helped to patrol the streets, but never engaged Onslaught directly. The same holds true for the Beast. Once he was freed from the Dark Beast’s lair, he joined the heroes in the Baxter Building, where he watched over the wounded and helped the other scientific minds to work on the armors. However, due to his week-long imprisonment, he probably wasn’t in fighting shape.
With the X-Men all busy, their house-guests, X-Force, were left with the task to watch over Nate Grey, X-Man. However, despite Domino II’s best efforts, Caliban, Meltdown, Shatterstar, Siryn and Sunspot couldn’t do much when Mr. Sinister invaded the mansion. Returning from a brief leave of absence, Warpath, with his girlfriend Risque in tow, failed too.
X-Factor weren’t even given a specific task. They stumbled onto Onslaught’s plans more or less by coincidence. Registering odd signals from a Sentinel processing plant, Forge, Polaris, Shard and Wild Child were unaware that their “ally“ Random was actually working for the Dark Beast, and in turn, Onslaught. X-Factor not only came too late to stop Onslaught’s reprogrammed Sentinels being launched; two of their reluctant members, Mystique and Sabretooth, were even approached about switching sides.
That not only the X-Men have a large number of friends and allies became apparent when the Baxter Building was under attack by ghostly manifestations of many of the Fantastic Four’s arch-enemies, sent to them by Onslaught. Agatha Harkness, She-Hulk, Alicia Masters and even her stepfather, the Puppet Master all did their best to help, just as staff member Ant-Man II would have done, had he not been injured when Onslaught’s EMP wave fried the cybernetics in his helmet. Yet, with the Inhumans’ Royal Family (Black Bolt, Medusa Gorgon and Karnak) and the remainder of the Fantastic Force (Huntara, Devlor and Vibraxas) showing up, the situation was quickly brought under control.
Another character often associated with the Fantastic Four would be Uatu, the Watcher, who revealed his presence only to Apocalypse and his scribe, Ozymandias, while observing the entire crisis. One could think that Gateway had sworn a similar oath of non-interference, given his staying silent all the time, but Wolverine and his friend Elektra would eventually get the old aborigine to reveal to them Onslaught’s origin. At first Logan blamed himself for the small part he had in it, but with the help of Stick, Elektra’s mentor, he soon got over it.
The Juggernaut was the first to feel the full wrath of Onslaught when he was entrapped inside the gem of Cyttorak. Other villains didn’t fare much better in their encounters with Onslaught. The evil entity tossed Sebastian Shaw and Tessa aside like flies, when he came to bring Holocaust away from them. In fact, Onslaught had lured some other villains to his side, though they never made it into the actual crossover. The London Hellfire Club’s Black Queen, Ms. Steed, obviously could not participate, for she was arrested by the local authorities. With Blob and the Mimic, one can only assume that Onslaught deemed them no longer necessary and simply let go of them.
The final section covers all other characters that made an appearance during the crossover, though none of them were too important in the overall picture.
For example, the Green Goblin, Peter Parker, Spider-Man II (Ben Reilly) and the Punisher were all seen fighting the Sentinels in the streets of New York. However, their efforts weren’t coordinated with the actions of the other heroes. At least they could do something, opposed to reporters such as J. Jonah Jameson, Robbie Robertson, Trish Tilby and innocent bystanders Foggy Nelson and Karen Page, who could only hope that the heroes would find a way to beat the mysterious Onslaught.
Unscathed by any of this, underneath the city, in the abandoned Morlock tunnels, Threnody was held hostage by the Marauders (Arclight, Harpoon, Scalphunter and Vertigo II) on Sinister’s command, to probe her for information on X-Man.
In Westchester, several magicians (Dr. Strange, Gomurr and Tar) joined forces, with the later two venturing into the Crimson Cosmos inside the Cyttorak gem to free the Juggernaut, who, despite the demoness Spite taunting him with bits of information, was still unaware of Onslaught’s true identity. They even had to oppose Cyttorak himself along the way.
Several hundreds miles away, the effects of Onslaught’s actions were still felt... by Generation X. Returning from a mission, Emma Frost suddenly felt some evil presence starting to influence her, causing her to act rather irrationally. Not wanting to lose another squad of students, she mentally took control of Jubilee, Synch, Husk and M and brought then to a safehouse in Canada, until Banshee along with some help by Alpha Flight’s Sasquatch could snap her back to her senses. Back at the Massachusetts Academy, Chamber found his powers no longer worked due to the chaos on the astral plane. As he experienced some strange spells of weakness, Chamber even had to rely on his teammate Skin to keep him alive.
Across the pond, Excalibur learned of Onslaught when they received Jean Grey’s emergency message. However, Nightcrawler, Colossus, Meggan, Shadowcat and Pete Wisdom could only briefly discuss the situation as the team were already facing their own problems.