WARNING: The following contains spoilers for Black Widow, now playing in theaters and streaming on Disney+ Premier Access.
In the Marvel Cinematic Universe, it's safe to say Chris Evans' Steve Rogers is one of the strongest heroes. The super soldier's fought elite killer robots, aliens, gods and, of course, Thanos, proving that the SSR and Dr. Erskine's serum was indeed something spectacular. It really did turn him into the perfect war specimen, so much so that Falcon and the Winter Soldier had a chemical arms race for vials to create the next Steve. However, Black Widow introduces another super soldier in the MCU, and this one is even stronger than Captain America.
It's Alexei Shostakov (David Harbour), the undercover agent that the Red Room planted in Ohio during the '90s to steal intel from a S.H.I.E.L.D. research facility. Russia's "first and only super soldier" was faking being a family with Melina, as well as the young Natasha and Yelena, in the opening act of Black Widow. They fled once he stole the research and burned the facility down, and when they got to the airfield, his true grit emerged.
Alexei chucked a truck away with ease to clear a path for Melina to pilot a small plane to Cuba, and as he shot the incoming S.H.I.E.L.D. agents, he was also able to run with the plane on the tarmac. He then latched onto the wing while still firing on his opponents, reminding viewers of Steve leaping onto various moving vehicles in The First Avenger. Steve struggled just to hold on at times, but Alexei is unflinching and effortless, smiling after they take off and escape. It's a comical scene, but it subtly teases just how powerful he is.
Later on in Black Widow, as he breaks out of a wintery Russian prison, Alexei's shown smashing walls and scaling the compound like an animal. He does so quickly, evoking shades of Steve, but the thing is, Alexei's now out of shape. Thus, one has to imagine he'd be even better if he were fit or conditioned for years like Cap was to be a true soldier. Granted, he probably did receive some training before he became the Red Guardian, but there's clearly something special about his raw strength, even in his unrefined state.
In the comics, Red Guardian was given his own variant of the super soldier serum that enhanced his strength, endurance and abilities immensely. Alexei debuted in 1967's Avengers Vol. 1 #43 and it's revealed that his death was faked when he was married to Natasha Romanoff. While she went on to become Black Widow and then defected, he was turned into the Russian equivalent of Captain America. He was trained rigorously and attacked Earth's Mightiest Heroes, only to switch sides and help them once he saw Natasha and remembered their love.
In the MCU, Alexei may have been part of such a program before and after the Ohio mission. At some point, he was imprisoned by Dreykov, so he might not have followed through on becoming the perfect soldier for the Red Room, or perhaps he was just disobedient in general. Thus, without that discipline, he might not ever have lived up to his potential and avoided being finessed. Given his propensity to eat and drink in Black Widow, this seems entirely plausible.
The thing is, if this serum can keep an unfit Alexei so strong, as seen with how he handles himself fighting Taskmaster in the finale, it might provide more base brute strength than other serums on the market. One can't help but wonder if there's more of this serum out there, if it's been perfected, if it's connected to Isaiah Bradley and how strong might its subjects be with Steve's training. It could pave the way for more super soldiers for Sam Wilson, Bucky Barnes and even Baron Zemo to someday pursue.
It is also possible that Red Room boss Dreykov, who loves chemical experiments and mind control technology, may have taken Alexei's blood. He could have retro-engineered it to sell on the black market, so with this shrouded in mystery, destruction could be on its way. It could be something for John Walker/U.S. Agent, Valentina and Yelena to track with their own Dark Avengers team, creating intrigue as to what other world powers have been cooking up for their armies.
Directed by Cate Shortland, Black Widow stars Scarlett Johansson, Florence Pugh, David Harbour, O-T Fagbenle and Rachel Weisz, with William Hurt and Ray Winstone. The film is playing in theaters and on Disney+ Premier Access.