Throughout the history of the Marvel Universe, various figures have been retconned and revealed to be connected to one of its most nefarious organizations: the Weapon Plus program, an institution whose experiments have turned its subjects into living weapons.
Its first products included the artificially created mutants of The World. But its most famous success stories are Deadpool and Wolverine, aka Weapon X. However, plenty of other major Marvel characters have been revealed to be results of the program, including some heroes that, technically, predate Wolverine's connection. Here are the heroes who have quietly been connected to Weapon Plus over the years.
Weapon I: Captain America
As revealed in Weapon X #23 (by Frank Tieri and Tom Mandrake), the Weapon Plus program was actually descended from the excitement the government had over the results of the World War II-era Project Rebirth - the same program that granted Steve Rogers enhanced physical abilities, turning him into Captain America. It was this success that spurred further experimentation within the program and resulted in Captain America retroactively being designated as Weapon I when the Weapon Plus program began in earnest.
Weapon II: The Brute Force
Weapon II was an attempt to weaponize a number of animals, cybernetically them to serve as living weapons. This resulted in both Weapon II (a mechanically improved squirrel with razor-sharp metal claws) and the Brute Force, a band of hyper-intelligent animal soldiers who eventually ended up in stasis until Wolverine and Captain America found them in Wolverine & Captain America: Weapon Plus (by Ethan Sacks and Diogenes Neves).
Weapon III: the Skinless Man
Initially listed in New X-Men as being focused primarily on animal test subjects, Weapon III was revealed to have had one successful graduate: Harry Pizer, aka the Skinless Man. First appearing in Uncanny X-Force #21 (by Rick Remender and Greg Tocchini), Harry had elastic and flexible skin, which the Weapon Plus program enhanced. The malicious Pizer eventually learned to control his muscle ligaments as tendrils after he was skinned by the Captain Britain Corps. A hated foe of Fantomex, the Skinless Man even briefly killed the hero before being killed himself by Deadpool.
Weapon IV: Man-Thing
Weapon IV was eventually revealed in Wolverine & Captain America: Weapon Plus to have been connected to Project Sulfur. This attempt to control and weaponize terra-flornics resulted in the head scientist on the project, Ted Sallis, experimenting with the SO-2 Serum, which in turn led to his transformation into the monstrous Man-Thing. Although Sallis would escape into the wilds of the Marvel Universe, his experiments eventually resulted in the creation of figures like Man-Slaughter, who would go on to star in X-Force.
Weapon V: Grendel
Absolute Carnage: Weapon Plus #1 (by Ethan Sacks, Jed MacKay and Stefano Raffaele) revealed that, in 1965, a symbiote dragon was discovered frozen in the arctic. Codenamed Grendel, Nick Fury and his team experimented on the alien substance and facilitated the creation of the Sym-Soldiers for S.H.I.E.L.D. - effectively starting Weapon V, later dubbed Weapon Venom. Deployed during the course of the Vietnam War, the Sym-Soldiers proved uncontrollable and violent. The program was shut down, with a reawakened Grendel playing a role in Absolute Carnage and the ensuing King in Black storylines.
Weapon VI: Luke Cage
A veteran of the Vietnam War, Noah Burstein was revealed to have become involved with Weapon Plus in Wolverine & Captain America: Weapon Plus. His experiments on Mitchell Tanner (who later became the unhinged and racially motivated villain Warhawk) impressed Weapon Plus enough for them to encourage more experimentation. His next batch was tested on residents of Seagate Prison, with his most famous subject being Luke Cage, who was given considerably enhanced strength and durability, becoming a major Marvel hero in his own right.
Weapon VII: Nuke
Dubbed "Project: Homegrown," Weapon VII was technically introduced during the Daredevil story arc, "Born Again," by Frank Miller and David Mazzucchelli. Eventually revealed to be a part of the Weapon Plus program, the only survivor of the process was the violent Frank Simpson. Enhanced with armored implants into his skin and conditioned with a series of adrenaline pills, he was given the codename Nuke and became a government agent tasked with completing dark, clandestine operations. He was believed dead following his battle with Daredevil in "Born Again," but was later revealed to be alive, leading him to spend time with the Thunderbolts.
Weapon VIII: The Sleeper Agent Program
Weapon VIII remains, perhaps, the most mysterious offshoot of the Weapons Plus Program. Teased in New X-Men #145 (by Grant Morrison and Chris Bachalo), Weapon VIII appears to be a host of enhanced assassins and sleeper agents. Controlled through the use of drugs and hypnosis, the soldiers are seeded into the world, poised and prepared to assist "Super Sentinels" such as Fantomex and Ultimaton in their purpose of wiping out mutantkind. The products of Weapon VIII have yet to be formally introduced, leaving a hole in the history of the program - and the potential for these sleeper agents to one day be activated.
Weapon IX: Typhoid Mary
Very little is known about the full history of Weapon IX, save for the confirmation that it took place in Wolverine & Captain America: Weapon Plus. Dubbed Project Psyche, it was the last program before the one involving Wolverine, and produced Typhoid Mary. A powerful mutant with multiple personas, Mary's volatile powers and training made her one of the deadliest products of the program, and she continues to operate as a villainous assassin as the wife of Wilson Fisk, aka the Kingpin.