WARNING: The following contains major spoilers for Black Widow, now in theaters and on Disney+ Premier Access.
One of the most fun and dynamic characters to debut in Black Widow was the Russian super soldier, Alexei Shostakov, aka Red Guardian. He loyally served his country and the politician Dreykov, who then sent him to prison for an undisclosed reason. His adoptive daughters, Natasha and Yelena, broke him out of jail. But shortly before his escape, he was seen in the prison mess, arm wrestling other inmates while being tattooed.
The scene illustrates just how tough Alexei is, as he can casually overpower other convicts without even disrupting the tattoo artist's work. However, what many people might not realize is that the man inking his back seems to be another Marvel villain: Niko Constantin, the Wolf Spider.
Many Marvel fans will be unfamiliar with the Wolf Spider, as he is a fairly obscure villain. The character debuted in Captain America #617 by Ed Brubaker and Butch Guice, part of the Captain America: Prisoner of War story, in which Bucky Barnes (who had replaced Steve Rogers as Captain America) was framed for a crime, extradited to Russia and locked in a gulag. While incarcerated, Bucky encountered a prison gang called the Wolf Spiders, led by Niko Constantin. In a flashback, it was revealed that the Wolf Spiders were the male equivalent of the Black Widow program. None of the candidates were deemed successful. However, Niko surpassed all of the physical requirements, only failing because of his psych evaluations, which revealed he was likely a psychopath.
It is worth noting that many aspects of the prison sequence in Black Widow are apparently inspired by Captain America: Prisoner of War, substituting Red Guardian for Bucky. Both Bucky and Red Guardian are imprisoned on falsified charges (presumably, in Alexei's case), have a confrontation with "Ursa" and are finally rescued when Natasha arrives by helicopter. It appears that the tattoo artist might be a reference to Niko Constantin, the only Wolf Spider. The biggest clue to this is the massive spider inked on his neck, but he also has a similar haircut and facial features to the comic depiction of Niko. He is surrounded by a group of men, who stand apart from those close to Red Guardian, apparently members of his gang. When Red Guardian gets up to retrieve his mail, two of the men keep their attention fixed on the tattoo artist.
The final clue is the tattoo gun itself. In the comic, Niko betrayed Bucky after offering to help him. Bucky's last words to Niko were to ask, "is there anyone in here who isn't a backstabbin' piece of--?" In Black Widow, Red Guardian is literally being stabbed in the back with the tattoo gun's electric needles.
Normally, such an obscure character would not even be considered, but Marvel has been drawing from quite a number of such characters lately, and this prison scene is clearly inspired by Captain America: Prisoner of War. Also, the main plot of Black Widow concerns stopping the Red Room and shutting down the Black Widow program. That makes the inclusion of the only male counterpart to the Black Widow program a thematically relevant Easter egg. He may only have had a small appearance in the film, but there is no denying that this character quite literally left his mark.
Starring Scarlett Johansson, Black Widow is playing in theaters and on Disney+ Premiere Access.