In addition to breaking 2021 box-office records and bringing the Marvel Cinematic Universe back into movie theaters, Cate Shortland's Black Widow brings Yelena Belova into the MCU for the first time. Yelena, who trained with Black Widow in the Red Room, made her first comics appearance in 1999's Inhumans #5 by Paul Jenkins and Jae Lee and would eventually go on to fight crime as the Black Widow for a time. The assassin has a sordid past with the Avengers, but she's also worked with other Marvel heroes including Blade the vampire hunter.
Yelena and Blade teamed up with an assortment of other heroes to form the Vanguard, a top-secret government task force in charge of espionage and assassinations, in Marc Guggenheim, Dave Wilkins and Tony Washington's 2007 "Vanguard" - a story serialized throughout twelve issues of Marvel Comics Presents. The Daywalker and the Russian assassin were joined by Micromax, a mutant with the power to change sizes; Dominic Fortune, a flying mercenary; Colonel America, a telekinetic super-soldier; and Retcon, a telepath.
The clandestine organization was so secret that even the president of the United States was unaware of their existence until Detective Stacy Dolan stumbled upon them while investigating a homicide in New York City. Trenton Craft, aka Colonel America, was shot in the chest in his home in New York, and the only evidence the police could find was one of Yelena's fingerprints. It later turned out that detective Dolan had been hypnotized by a man named Jafar Yoosuf who made her shoot Trenton. But in another twist, Trenton had used his telekinetic powers to survive the gunshots, and he returned to kill Dolan as well as the members of Vanguard to preserve the organization's secrecy. Retcon used her powers to make Colonel America believe that he successfully killed them, while Blade, Yelena and the others made their escape.
After fleeing a murderous Colonel America, the members of Vanguard faked their own deaths and went their separate ways. Clearly neither Yelena nor Blade were natural-born team players, so it is safe to assume that they adjusted to their solitary lives fairly well. But, their brief time working together as government agents sets a precedent for their ability to cooperate with each other, which could be an important detail as events continue to unfold in the MCU.
As Marvel continues to tease the appearance of the Thunderbolts in the MCU and prepares to begin production on a new Blade film, it is entirely possible that both Blade and Yelena could meet in the movie universe. Events in Black Widow and The Falcon and the Winter Soldier suggest that Yelena may eventually join Valentina Allegra de Fontaine's Dark Avengers, a team of often morally ambiguous anti-heroes. But the parallels between the Dark Avengers and the Thunderbolts, a team historically made up of pseudo-reformed villains and mercenaries often lead by either Black Widow or Task Master, leave room for some overlap between the two teams. While Blade was never on either team, his comic book history with Yelena may be a great way to connect him to the Thunderbolts.
While the Vanguard was a fairly short-lived team of heroes, its impact on the dynamics between characters in comics and the films could be long-lasting. At the very least, it highlights the similarities between Blade and Yelena Belova, who are both extremely capable killers who thrive in ethical gray areas. It isn't often that Blade takes a break from his war on vampires to kill humans, so Yelena is one of the rare people in the Marvel Universe who has collaborated with the Daywalker on something other than tracking the undead.