Romanogers

Romanogers is the het ship between Steve Rogers and Natasha Romanoff in the Marvel fandom. (Careful, this post contains spoilers from recent MCU movies, including Avengers: Infinity War)

Comics
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Captain America and Black Widow had a son together named James Rogers.

Marvel Universe (Earth-616)

Films
Marvel Cinematic Universe (Earth-199999) The Avengers

Steve and Natasha first meet during the events of "The Avengers" on the Helicarrier when they are introduced by Agent Phil Coulson. They worked cohesively as a team defending New York City. There were few interactions between them, while they were fighting or checking up on each other.

Captain America: The Winter Soldier

After the Battle of New York their relationship progesses to that of partners for different missions, probably for two years. One mission, to retrieve data and hostages from the Lemurian Star was shown at the beginning of "Captain America: The Winter Soldier." The mission is shown to sow discord between Rogers and Romanoff due to the fact Romanoff received a different mission than Rogers from Fury and did not share the details. After rescuing the S.H.I.E.L.D. hostages Steve is given a USB drive, which had been filled with some S.H.I.E.L.D. intelligence earlier by Natasha. Lately Steve hides the USB in a vending machine at the hospital. But when he visits the hospital again, he finds out that the USB is gone. Natasha appears from behind and reveals that she had taken it, and he angrily asks her what she knows about all that has happened. She tells him that the masked man is an assassin known as the Winter Soldier, and she had encountered him once before. She decides to follow Rogers. Undercover they go to an Apple store to see if they can access any of the valuable information on the USB. They act as an engaged couple, and while they are riding escalator, Natasha kisses him in order to hide from Hydra agents. Natasha later helps him gets shot fighting the Winter Soldier, but goes on to help defeat Hydra leader Alexander Pierce.

Avengers: Age of Ultron

In Age of Ultron, it seems Romanogers is derailed due to the short relationship between Bruce Banner and Natasha Romanoff. Steve Rogers, upon watching the two flirt, even declares that he's 'seen her flirting up close,' advising Banner and the two of them that they 'deserve a win' and should go forward in their relationship. They work together many times throughout the movie, particularly during the final battle in Sokovia, where Rogers claims he will not leave without evacuating every civilian, wherein Romanoff states she will not leave either with the phrase "where else am I gonna get a view like this?" At the end of the movie, Romanoff and Rogers begin training of the new Avengers recruits, with Steve uttering the classic phrase "Avengers Assemble!"

Captain America: Civil War

Natasha and Steve take opposing sides on the Sokovia Accords, but she meets him in London to comfort him about Peggy Carter's death. In a deleted scene, she even shares information about the answers she went looking for at the end of Winter Soldier and about her parents. The two end up battling each other at the airport, but Natasha eventually shoots the Black Panther, T'Challa, with her Widow's Bite allowing Steve and Bucky to escape.

Avengers: Infinity War

Taking place a few years after the events of Civil War, Steve and Natasha appear to have reconciled their differences and are first shown saving Wanda and the Vision from Proxima Midnight and Thanos's other minions coming to collect the stone. They travel to see Rhodey where Natasha comes face to face with Bruce Banner but only acknowledges him with an awkward "hi." Planning to have Shuri remove the Stone from Vision, they venture into Wakanda where Thanos attacks and uses the collected Infinity Stones to kill half of Earth's population. They are two of the select few MCU heroes left.