For years, it was thought the horrific experimentation that saw Wolverine’s skeleton laced with adamantium was part of the Weapon X Program - a government initiative that also led to the creation of other superhumans, like Deadpool. And while that’s still mostly true, one big revelation Logan has made of late is that the "X" in Weapon X is actually a Roman numeral, and that the entire project is just one phase of a larger program dating all the way back to WWII - the Weapon Plus Program.
In its several decades of existence, the secretive and shady Weapon Plus Program has served as the origin story for countless prominent superheroes, including some of Marvel Comics' best and brightest. That so many costumed crusaders share a common backstory perhaps shouldn’t come as a surprise - especially when it gives writers the opportunity to tie something together with Wolverine’s origin, easily one of the most iconic in comics.
Project Rebirth was a secret WWII-era program aimed at creating an army of Super Soldiers to win the war - but the lead scientist on the project, Dr. Abraham Erskine, was taken out by a Third Reich spy moments after Steve Rogers became Captain America. This left the United States with just one Super Soldier, a few experimental loose-ends, and a major hankering to create some new living weapons.
Under the guidance of Professor Truett Hudson, the Weapon Plus Program was born. Captain America was retroactively deemed “Weapon I,” but with the secrets to his transformation lost forever and he himself frozen in ice by that point, the program now had to go about finding new ways to make some government-sponsored superhumans.
Weapon II: Brute Force
Before Weapon Plus got back to experimenting on human beings, they decided to take a detour into the animal kingdom. Collaborating with a corporation specializing in cybernetics, the Weapon II program set about creating animal super soldiers, each with their own high-tech enhancements.
While the creature that officially took on the mantle of Weapon II was a squirrel with Wolverine-esque claws, the more notable graduates of the program were a team known as Brute Force. Made up of a bear, a lion, a dolphin, a kangaroo, and an eagle, each member of Brute Force gained the ability to speak, as well as increased strength and intelligence from their cybernetic enhancements. Amazingly, they’re still kicking around the Marvel Universe to this day.
Weapon III: Skinless Man
For the third phase of the Weapon Plus Program, the Professor Hudson and his team went back to experimenting on people - albeit, those who already came with their own built-in superpowers. Harry Pizer, a British mutant born with elastic and multisensory skin, was recruited into the program, where experimentation granted him even greater control over his epidermis.
Now a government-sponsored superpower, Pizer served as a spy throughout the Cold War, using his increased abilities to conduct espionage and steal information from important documents. Unfortunately, he also proved to have a sadistic side. He ended up shot and skinned by another, later Weapon Plus grad, Fantomex, leading to a new nickname - the Skinless Man.
The fourth iteration of the Weapon Plus Program went in a vastly different direction that previous attempts. With Dr. Ted Sallis at its head, “Project Sulfur” created something known as the SO-2 Serum, which was supposed to render soldiers impervious to all biochemical attacks. And it succeeded at that - though with the unfortunate side-effect of also turning them into horrible, leafy monsters.
The first such result of Weapon IV was Jackson Strode, who became known as Man-Slaughter and went on several dangerous missions for the United States. Later, Sallis himself came into contact with the serum and became the entity known as Man-Thing - a heroic, but hideous, beast who burns anyone who feels fear, and has settled into a role as the guardian of the Nexus of Realities.