Multiple Man was the basis for En Sabah Nuhr's armies in the Age of Apocalypse. The Eternal One's scientists experimented on Madrox's x-factor until he could produce nearly an infinite amount of duplicates, all loyal to Apocalypse. The Madri were his elite guard and foot soldiers, serving him with a religious fervor in all things. The original Jamie Madrox was kept in seclusion, and had become reduced to a broken shell of a man. When the X-Men found Madrox, he made a heroic sacrifice and willed himself to die, resulting in the deaths of all the Madri throughout Apocalypse's empire, crippling many of his operations and greatly reducing the manpower of his armies.
In the Earth X timeline, Jamie Madrox was struck by the curse of the Wendigo. Trying to survive in the wild, with the ever-changing climate of the Savage Land and the rest of the world, Madrox ultimately resorted to eating the flesh of one of his own duplicates in order to keep from starvation. This transformed all of him into the Wendigo and he became a lethal predator, with his bodies and appetite constantly multiplying. The Wendigos consistently attacked the caravan of Wakanda's people and Ani-Men, guided by Scott Summers and his new X-Men. The heroes ultimately established a fiery trap for the Wendigos and discovered Multiple Man's new identity when one of the Wendigos was briefly in human form. In the end, he/they had to be killed in order to save the caravan.
Multiple Man’s counterpart of the Ultimate universe sided with Magneto and used his power to create duplicates of himself to lead an art heist at The Louvre in Paris. Apparently, he also staged an entire protest on his own, and can create up to 28 duplicates of himself. However, dividing his consciousness over so many bodies takes its toll on him. Madrox worked with Magneto's Brotherhood for some time, and used his selves as suicide bombers during the Ultimatum event. At one point, it appeared as if the real Madrox was an innocent kept under the hypnotic control of Lorelei for the Brotherhood. He was kept safe and oblivious while his duplicates were turned out as fodder for Magneto. However, after Wolverine killed this Jamie Madrox, the Madri still appeared as Quicksilver's work force, indicating that wasn't Jamie-Prime.
THE PLOT OF THE MULTIPLE MAN SERIES
After the death of Jamie-Prime because of the Terrigen Mists, all his duplicates seemingly died as well. However, months later, one final Jamie was discovered in an airtight laboratory on Muir Island. He initially claimed to be Jamie's scientific side, working on an experimental serum that might allow a new Jamie-Prime to be chosen from among the dupes, should Jamie-Prime die. He passed his work on to Hank McCoy, who hoped to carry it through to completion, but there was a catch. This Jamie was undergoing catastrophic organ failure, apparently as a delayed response to Jamie-Prime's death which kicked in after he left the airtight environment. Beast believed he could finish the serum, but not before this Jamie died. Jamie made Beast promise to complete their work no matter what. He then tracked down Bishop, knocked him unconscious and stole his time travel device.
You see, this Jamie wasn't actually Madrox's scientific side -- he was a borderline sociopath manifestation of Jamie's evil, megalomaniacal urges. He had been locked away for being evil, not to conduct laboratory work, and the serum was his last ditch attempt to assert himself. When this Jamie was conceived isn't certain. He later claimed he had never met Layla Miller, but was clearly from the time period after Jamie's dupes started showing unique personalities. In any case, Evil Jamie used Bishop's time machine to literally borrow time, leaping ahead in the timestream to when Beast finished the serum. He used it on himself to become the new Jamie-Prime, saving his life and allowing him to produce new duplicates. He then killed and skinned Beast, produced an army of Madrox duplicates, and conquered the world as Emperor Madrox.
Fifteen years in the future, Emperor Madrox was opposed by a small resistance led by David Miller, the teenaged son of Jamie Madrox and Layla Miller. The emperor and his chief enforcer, General Madrox, destroyed the resistance and executed David Miller. The resistance had included several duplicates whose divergent personalities deviated from Emperor Madrox enough that they flipped back to being "good." Many were killed, but one Jamie serving as a key figure in the resistance survived, and the general brought this Madrox before the emperor. This Resistance Madrox told Emperor Madrox he would either change his ways now or kill the resistor and learn to regret it later. The emperor didn't believe the warning, and decapitated this Jamie on the spot.
Perturbed by the fact that this Jamie seemed slightly older than him, the Emperor began to worry about the possibility of time travel being used against him. The General informed him that they had already sent a Soldier back in time to ensure Beast completed the serum without any hitches. Nevertheless, the Emperor demanded he be left alone. Staring into his own lifeless eyes, Emperor Madrox did begin to feel remorse. He regretted what he had made of his life and decided to prevent the rise of his empire. Emperor Madrox put on the Resistance Madrox's clothes and traveled back in time. He arrived fifteen minutes after Beast first told him he was dying and maybe five minutes after clocking Bishop and stealing his time machine. Emperor Madrox absorbed Soldier Madrox and told Beast not to make the serum.
As Madrox tried to explain himself to Beast, Bishop and the other X-Men, the mansion was attacked by four radically divergent Jamies: a Hulk Madrox, a Madrox Master of the Mystic Arts, a Weapon Plus Madrox and a Cable Madrox with a Warlock symbiote. In the future, just before he was captured, Resistance Madrox had dispatched five "good" Jamies through time to gather allies, resources, or skills to aid in the uprising against Emperor Madrox. These four were the same Jamies, having completed their quests and come back in time for the initial recruitment of Resistance Madrox to fulfill the time loop and come aid them against Emperor Madrox. As they all returned to fifteen years in the future, Emperor Madrox therefore became Resistance Madrox, aiding the Madrox Pack against his own slightly younger self. Emperor / Resistance Madrox met the Pack's younger selves, sent them on their missions and was ultimately beheaded by Emperor Madrox, completing this second time loop.
Except, no. When General Madrox found the throne room empty and the emperor missing, he realized Emperor Madrox intended to prevent the serum from being created, wiping out the future Jamies' lives and empire. General Madrox and the Madrox Army arrived back in the present moments after E/R Madrox and the Madrox Pack traveled into the future. Bishop had planted a bomb on one of the Madri before they left, so he detonated it to prevent this timeline from coming to pass. However, because Resistance Madrox had already lived through that time as Emperor Madrox before leaving again with Bishop's bomb, the explosion only made things more complicated. It destroyed Emperor Madrox's future civilization, leaving General Madrox and his army in the past unanchored in time. A version of Resistance Madrox and the Madrox Pack were at the epicenter of that explosion and died, but another version also arrived in the future created by the explosion. The future that was the past of Emperor Madrox where he experienced regret after killing his future self no longer existed, and so this Madrox's fate was no longer sealed by the time loop.
Emperor Madrox and the Madrox Pack returned to the present to find the X-Men overrun by General Madrox and the Madrox Army. The general forced Beast to produce the serum faster and applied it to himself. Now both the emperor and the general were "Jamie-Prime." Each of them tried to absorb the other, creating a composite Jamie-Prime with two warring personalities. Emperor Madrox felt he couldn't fight forever against the General, and so he begged the Hulk Madrox to kill him. With the composite Jamie-Prime dead, all the Madrox Pack and Madrox Army duplicates died as well, leaving behind a field of corpses. Jamie Madrox was truly dead this time, forever and ever.
Two days later, Jamie Madrox returned. The resistance had sent out five time-traveling duplicates, but only four had previously returned. This Jamie had given up on his mission and just lived in an alternate future for some time working at a tiki bar until the timeline went sour. (He was now branded with an 'M' tattoo, indicating it was something similar to the Days of Future Past camps.) He tried jumping back to his future timeline only to find it wiped out, and so returned to the present. As he caught the X-Men up and walked away, this Jamie found the last of Beast's serum, indicating he injected himself to become the latest Jamie-Prime.