Black Widow

Natalia Alianovna "Natasha" Romanov/Romanoff, also known as Black Widow, is one of the most talented spies and assassins in the entire world and a founding member of the Avengers. Originally a KGB operative and dangerous assassin, Romanoff was recruited into S.H.I.E.L.D. by Clint Barton. Having extensive mastery in martial arts and armed with her Widow's Bite, Black Widow became one of S.H.I.E.L.D.'s most efficient agents. During one mission, she was sent undercover into Stark Industries to watch Tony Stark due to the fear that he was dying. During this mission, Romanoff assisted Stark with defeating Ivan Vanko's terrorist plots against him.

When Loki declared war on the Earth, Black Widow was recruited into the Avengers after Hawkeye had just been enthralled by Loki. Romanoff assisted in recruiting Stark and Bruce Banner into the team while they tracked down and attempted to capture Loki, eventually saving Barton from his grasp. Once Loki's entire plan had been uncovered, Romanoff joined the team during the Battle of New York and was instrumental in destroying the portal over the city which had been created by the Tesseract, effectively ending the entire invasion while Loki was defeated and captured.

In the wake of the Avengers successfully defeating Loki, Romanoff had continued her work with S.H.I.E.L.D., this time working with Captain America. While working together, Romanoff and Rogers uncovered a conspiracy following an assassination attempt on Nick Fury, which had eventually led to them discovering that HYDRA had somehow been infiltrating their entire organization. Despite the efforts of the Winter Soldier to stop them, Romanoff helped expose Alexander Pierce's evil schemes to the world, which also resulted in all of her own morally dubious history being revealed. As a result, Romanoff was forced into dropping off the grid again and began rebuilding her cover.

Romanoff helped to try and bring down any more HYDRA goons by Nick Fury and came across an old HYDRA cell in Switzerland. Investigating this place with Barton, they both discovered the cyrogenic frozen body of Romanoff's great-aunt Rosemary Harlow.

Romanoff eventually re-joined the Avengers, working to bring down various HYDRA cells across the world and assisting in the capture of Wolfgang von Strucker. However, before she could form a romantic relationship with Banner, the rogue artificial intelligence Ultron was created by Stark and Banner, forcing Romanoff and the rest of their team to join together and defeat him. Despite being captured, Romanoff was able to inform the team of Ultron's location on Sokovia, resulting in a final battle in which the Avengers had defeated Ultron once and for all. Unlike most members of the original Avengers, Black Widow remained a member while forming the second incarnation of the team.

As many of the governments of the world had demanded the Avengers to sign the Sokovia Accords in the wake of their recent battles, Romanoff agreed to their terms and signed the Accords. She later joined Iron Man in a fight against Captain America due to his disagreements with the Accords and his criminal activities with the Winter Soldier who Rogers was attempting to protect. As the two Avengers' factions fought against each other, Romanoff betrayed Iron Man's team in order to assist Captain America to find the instigator of the team's fight. As a result, Black Widow had to escape from the government for aiding Rogers, while being on the run, Romanoff soon joined him and Wilson in stopping terrorists.