With the smash success of Moon Knight, Marc Spector has proven that Marvel heroes don't necessarily need to start on the right track. While there will always be the noble Steve Rogers, who embodied heroic ideals from the start, not every good guy starts on the good side. Some of them can start on a different and darker path that makes their rise to heroism even more admirable.
While Marvel Comics has many heroes that started in low places, many spent many years moonlighting as assassins or mercenaries. While today, many of these heroes are beloved by comic readers, their darker origins need to be remembered and celebrated as they achieve greater heroic heights.
Elektra
Though she recently took up the Daredevil mantle, Elektra was originally an assassin trained by both Stick and the Hand and served as a for-hire mercenary working odd jobs across the world. Her skill made her an extraordinary asset to anyone who needed her services, and her relationship with Daredevil just helped to increase her connections.
Her background makes her nature as a hero all the more interesting. Much like Matt Murdock used Daredevil to help cope with his doubts and guilt, Elektra used the mantle to prove that she was more than a mercenary. Desperate to prove that she was not all terrible, her need for redemption made her an extraordinary hero.
Fantomex
Created by Weapon Plus, Fantomex is a deadly assassin with a feigned French accent and an entirely boisterous personality. More often than not using his skill to take on Weapon Plus and its agents, Fantomex is a warrior with a cybernetic mind and a nervous system that happens to be kept in an exterior device called E.V.A.
Often using his experience as a thief and assassin in pursuit of more heroic goals today, Fantomex is also part-android, thanks to Weapon Plus experimentation, so the merc-turned-hero may be turning toward the machine side of the mutant-machine war sooner rather than later.
Domino
An extremely powerful member of X-Force, Domino wasn't always just a defender of Krakoa. A supersoldier survivor of Project Armageddon, Domino spent many years as a mercenary, both protecting at-risk figures and taking out her opposition for a paycheck.
It was only after meeting Cable that Domino made the move toward the light. Joining the first X-Force, Domino proved to be a valuable asset with her willingness to dirty her hands for the benefit of mutant-kind. On Krakoa, she has proven capable of using her luck-based powers to serve as the spy she was trained to be as a member of Krakoa's mutant CIA.
Daken
A mercenary who had been a major part of several less-than-legal associations, the son of Wolverine found himself working as a mercenary for decades. First taught by the villain Romulus, he became a skilled killer and a cruel manipulator, but his experiences under the Red Right Hand, Norman Osborn, and Malcolm Colcord made him a mercenary.
Now, having sought amnesty through Krakoa, Daken is an X-Factor investigator and a Marauder, dedicated to helping mutants around the world. While his background still makes him a bloodthirsty and vengeful character, it also means he can be a heavy hitter whenever his teams need him to be.
Gamora
While she's often shameless about the things she's done, Gamora is an assassin raised by Thanos with the express goal of being his weapon. Though today, Gamora is a member of the Guardians of the Galaxy and found love from Nova and Star-Lord, she spent many years serving without question.
Gamora's history hardened her, and her harsh perspective of the galaxy meant that she could use deadly methods without much remorse. With hand-to-hand combat skills that let her survive an individual confrontation with Ronan the Accuser, she can take on anyone in the galaxy. It is, after all, how she managed to kill Thanos.
Black Widow
A Red Room agent and former KGB member, the Black Widow was often a thorn in Iron Man's side. Or, really, a stinger. Her background meant that she was often sent on assassination missions, targeting high-value political agents for the Soviet Union's benefit.
Her work as a mercenary afforded the Black Widow many enemies through the years, including Taskmaster, Madame Hydra, and Snapdragon. All skilled fighters of their accords, but none can compare to the Widow. She managed to use her experience as an assassin to fit in amongst gods and supersoldiers, and that's an impressive feat in and of itself.
X-23
The daughter of Wolverine and the product of genetic experimentation, Laura Kinney was created and trained by Weapon X to serve as the perfect weapon. Using her as a mercenary and assassin, Weapon X sent Kinney on numerous assignments of important political figures around the world.
Thankfully, Kinney eventually escaped from Weapon X's facility and managed to introduce herself to her biological father, Wolverine. Finally given the chance to have some semblance of safety, she took up the Wolverine mantle and spent years doing the same heroic work her father does.
Wolverine
An extremely skilled fighter who's killed some exceptionally powerful characters, Wolverine is known for his berserker rages, incredibly quick regenerative abilities, and his adamantium skeleton. But, under the command of the ninja Ogun and the immortal villain Romulus, Wolverine spent many years as a trained mercenary.
While his past often comes back to bite him, like when he discovered Daken's existence, it has also given him an edge in conflicts. Even when the other X-Men hesitate to kill, Wolverine is always ready to finish the job. After all, it's why he killed Moira, tried to kill Rachel Summers, and even tried to kill Cyclops.
Gambit
While Gambit is best known for his romance with Rogue, the smooth-talking X-Man was once a member of the Thieves Guild and spent a not-insignificant amount of time working under Mister Sinister as a mercenary. In fact, his responsibilities went so far as to involve him taking part in the infamous Mutant Massacre.
After the massacre, Gambit attempted to join the X-Men and quickly bonded with Rogue. Still, his history has caught up with him numerous times. After Rogue discovered his involvement, she nearly broke off their relationship, but thankfully the two persevered, and Gambit now uses his skills as a thief to steal Tarot cards from Saturnyne and take down Otherworldly threats.
Moon Knight
A mercenary who didn't have quite the same capacity for violence as his colleagues, Marc Spector was left for dead after being fatally wounded by his fellow mercenary, Bushman. Yet, after being saved by the Egyptian deity, Khonshu, Spector became the Moon Knight and began protecting the travelers of the night around the world.
His background often allows Moon Knight to get bloodier than most other heroes. Unafraid to get his hands dirty, he often leaves his villains terrified, which only makes him less respected by other less violent heroes in the Marvel universe.