The following contains spoilers for "What If... Captain Carter Were The First Avenger?"
The latest Disney Plus series from the Marvel Cinematic Universe continues the trend of giving fans something vastly different from the movies by riffing on them and a comic book anthology series. Each episode is set to see events in the MCU play out differently based on a single different decision being made in the movie universe. In the first episode of What If...?, that decision is Peggy Carter opting not to sit in the audience when Steve Rogers gets the super soldier serum in Captain America: The First Avenger.
Peggy ends up being the test subject instead when Steve is injured by the Hydra operative at the experiment. She takes on the mantle of Captain Carter as a result. That's not the only difference in how events play out though. As fans watch the animated series they will be able to catch a ton of references to the original movie and see just how they're spun for Peggy in her new role. The Easter eggs and parallels pile up very quickly.
The Watcher
The opening narration of the episode reveals a peek at the splintered worlds created by the Nexus Events hinted at in Loki. It also introduces the Watcher to the series, the being telling all of the alternate universe stories.
The Watcher is a Marvel comic book character. Just as the animated series promises, he observes the many Earths as their stories unfold. This isn't, however, the first time a Watcher appeared in the MCU. Fans will remember a Stan Lee cameo from Guardians of the Galaxy Vol. 2 featuring characters who resembled the Watcher. The idea in the scene was that all of Lee's cameos were the result of him informing on Earth. Like Captain Carter, the Watcher is set to be one of the main protagonists in What If...? The audience will surely see more of him.
Captain Carter References The First Avenger
Because Captain Carter's journey begins where Captain America's would have, the episode features a ton of references to his first MCU movie. Even shots created by the animators reference the events of the movie, like the zoom-in on the Hydra logo on Red Skull's car. There are a lot of little moments for fans to pick up on.
When Peggy Carter is infused with the super soldier serum and the vitarays, the pod opens to her in the exact same pose as Steve Rogers as he emerged. In fact, she gets a lot of Steve's moments in the movie. She knocks a punching bag clean off its hook when frustrated. Peggy and Steve even still have a conversation about dance partners.
One of the funnier nods is during the scene of Peggy's frustration in the gym. As Steve comments that she could be paraded around on a USO tour, she's horrified at the thought. That's exactly what the movies do to him. Even when Howard presents her with a costume, it was created with the idea of being used to sell war bonds.
Captain Carter Makes First Avenger Changes
Just as the episode makes some fun nods to The First Avenger, it also makes some specific changes. The changes demonstrate how effective Peggy would have been in the Captain Carter role while still honoring the movie.
Fans know that Steve doesn't get in contact with his air support for retrieval while on a rescue mission for the 10th because the radio is damaged in the fight. Peggy keeps her radio intact, and when she calls for support, it's Steve she gets. She also happens to get to the 107th before Hydra starts experimenting on Bucky since he's still with the other prisoners.
When the Howling Commandos board the train, Bucky doesn't fall to his supposed death. Instead, Peggy manages to grab him and pull him up by one arm. That prompts Bucky's quip about her almost ripping his arm off, a nod to his metallic arm in the MCU.
"We Don't Have All Day."
Steve Rogers first makes his "I can do this all day," remark in The First Avengers when cornered by a bully in an alley. It becomes one of his most quoted lines in the MCU, and gets referenced in a few other movies as well. That particular moment doesn't make it into this episode, but it does get a nod.
Bucky is the one to provide the nod, noting, "We don't have all day," when he thinks Steve is taking too long. It's a nice mirror to the friendship as it exists in the main timeline between Steve and Bucky since Bucky is the one to find him in the alley.
Colonel Flynn
Fans of the MCU might not recognize Colonel Flynn. He doesn't appear in the original movie. Instead, he appears to give Peggy Carter a hard time in the Agent Carter one shot. One shots were initially filmed and released as special features on the DVDs of Marvel movies.
This particular one shot features Peggy on a mission for the SSR after the events of The First Avenger. Whether it's canon in the MCU since it contradicts the Agent Carter television series is debatable. It was available as part of the special features on Iron Man 3's DVD release.
The Hydra Stomper
Though Steve is injured and unable to become Captain America, he still aids in the war effort with Captain Carter. He takes on the role of Hydra Stomper in an armored suit.
That suit is less of an Easter egg and a pretty in-your-face reference to Iron Man. It bears a strong resemblance to Tony Stark's first effort to create an Iron Man suit, long before he even has a name for it. The suit also bears a pretty strong resemblance to the Iron Giant. In this case, Howard Stark creates the Hydra Stomper, not his future son.
Hydra's Unleashed Monster
In the original movie, Red Skull falls through a portal opened by the Tesseract. He ends up on Vormir, waiting for someone to retrieve the Soul Stone. The portal opened here, however, brings something else to Earth instead.
The audience never gets a complete look at what comes through the portal, but it is a many-tentacled monster. Captain Carter spends a lot of time slicing through tentacles while Howard attempts to close the portal. The monster appears to be similar in design to the Abilisk that appears in Guardians of the Galaxy Vol. 2, but it also could be a nod to Shuma-Gorath from Marvel comics. The being hails from another dimension and tries to take over Earth multiple times. Of course, the tentacles could also simply be a nod to Hydra itself having a tentacled monster as its logo.
Captain Carter References Captain Britain
Though it's clear that Captain Carter is a rewrite of Captain America, the hero also provides a nod to a different Marvel comic book character. The design of the character's costume, for example, doesn't fall in line with existing Captain Carter in the comics. Instead, it's similar to Captain Britain, the English answer to Captain America.
The choice makes sense considering Peggy is also an English hero, despite working with primarily American forces. Likewise, her use of a sword in the climax of the episode, not just the Captain's shield, is another nod to Captain Britain, who carries a sword in the comics.