Episode 1 of Marvel’s Disney+ series "What If…?" introduced fans to one of the MCU’s most exciting heroines: Captain Carter. Exploring an alternate timeline following the birth of the multiverse in "Loki," "What If…?" Episode 1 delves into a world where Peggy Carter was given the super soldier serum instead of Steve Rogers.

Hayley Atwell, who has portrayed Peggy in MCU installments such as "Captain America: The First Avenger," "Avengers: Endgame" and "Agent Carter," reprises the iconic role for the animated series. But that’s not all. The multiverse will be front and center in upcoming MCU projects including "Spider-Man: No Way Home" and "Doctor Strange in the Multiverse of Madness." Fans could see Captain Carter make the leap from the animated Disney+ series and into live-action on the big screen.

Peggy’s character has held tons of potential ever since her 2011 debut in "The First Avenger." In an era of periodical sexism, Peggy shattered glass ceilings and battered boundaries to become one of the most influential pioneers in the MCU. Despite starring in her own series on ABC, however, Peggy’s awe-inspiring story is still largely untold. "The First Avenger" relegated her to a supporting character and a love interest for Steve Rogers (Chris Evans). "What If…?" reverses their dynamic by having Peggy take the serum and become Captain Carter, while Steve takes on a different mantle as the HYDRA-Stomper.

Whether Captain Carter will appear in live-action remains to be seen, but Marvel producer Brad Winderbaum has confirmed that she will appear again in Season 2 of "What If…?" The future looks bright for Captain Carter, and many fans are already anticipating her MCU return. Until then, here is everything you probably didn’t know about Marvel’s Peggy Carter.

Peggy’s TV series isn’t canon anymore

Peggy Carter wearing her iconic red hat

Peggy Carter’s story doesn’t end with Steve Rogers’ (supposed) death in "The First Avenger." The British spy went on to star in her own series, "Agent Carter," which ran for two seasons on ABC, spearheaded by series creators Christopher Markus and Stephen McFeely. The series picked up after the events of "The First Avenger," as well as the 2013 Marvel One-Shot "Agent Carter," which had Carter pursuing the Zodiac while facing sexism in her new job with the SSR.

The "Agent Carter" series was similar to that short film. Both feature Peggy’s struggle against sexism in 1940s America, as she forges a life and legacy as a secret agent. Despite its cancellation after two seasons, "Agent Carter" was well-received by fans and critics for continuing Peggy Carter’s story in the MCU after her break-out role in "The First Avenger."

"Agent Carter" contains a compelling story for one of Marvel’s best supporting characters … Or it would, if it was still canon. Marvel Studio’s "Legends" omits Peggy’s history from "Agent Carter," seemingly indicating that the ABC series has been given the same treatment as "Agents Of S.H.I.E.L.D," another Marvel show that featured Peggy in cameo appearances. Peggy is still a trailblazer, though her story in the main timeline has been trimmed to her appearances in "The First Avenger," "Captain America: The Winter Soldier," "Ant-Man," and "Avengers: Endgame," as well as the "Agent Carter" One-Shot.

She didn’t want to join the military initially

Peggy Carter shoots at a Hydra agent

Although the status of "Agent Carter" in the MCU might be shaky now (remember, it could still take place in an alternate timeline thanks to "Loki"), the series gave fans insight into Peggy Carter’s background, and who she originally wanted to be. Would you believe Peggy wasn’t always a trailblazer? According to "Agent Carter," she originally had no intention of defying gender roles in 1930s Britain. Her job with the British Royal Military consisted mostly of desk work, and when Peggy was offered a more active role with the Special Operations Executive, she turned it down.

Everything changed for Peggy when her beloved brother, Michael, died. She broke up with her fiancé, Fred Wells, despite their looming wedding. Peggy’s attitude changed as she accepted what her brother knew; she was a fighter, determined to change the world. After that, Peggy reversed her earlier decision to become a field agent and eventually joined MI5, before going to work with the Strategic Scientific Reserve — and Steve Rogers.

The death of her brother motivates her

Michael Carter, Peggy's brother

Understandably, Michael’s death continues to motivate Peggy as her story unfolds throughout the Marvel Cinematic Universe. His words of support inspire her to rebel against the life society wants her to have, and follow her true dream: making a difference in the world. In a way, Michael is an unsung MCU hero. Without him, audiences would never have met Agent Carter, let alone Captain Carter.

Flashbacks throughout "Agent Carter" reveal that it was Michael who urged Peggy to join the military. Peggy, content to marry and adhere to gender roles, rejects him at first. But when Michael dies while fighting in the war overseas, everything changes for Peggy. She accepts her brother’s advice and recommendation. Time will tell if Michael will be mentioned in a future MCU installment featuring Captain Carter… or if Peggy’s brother is another dropped plot point from "Agent Carter" to disappear into the ether.

Peggy rescues Dr. Erskine from Johan Schmidt prior to "The First Avenger"

Dr. Erskine talks with Steve Rogers

Dr. Abraham Erskine is integral in Steve’s transformation to Captain America — and without Peggy Carter, the two would never have met. Part 3 of the 2011 digital comic book series, "Captain America: First Vengeance," a collection of stories set around "Captain America: The First Avenger," delves into Erskine’s rescue from the Red Skull (aka Johan Schmidt). Peggy Carter disguises herself as a maid and infiltrates Castle Kaufmann. She frees Dr. Erskine and the two flee, before joining up with Colonel Philipps and Howard Stark.

Creator of the original super soldier serum, Dr. Erskine (played by Stanley Tucci) puts his talents to use working with the SSR. He oversees Steve’s recruitment after overhearing a conversation between Steve and Bucky during "The First Avenger." Erskine changes Steve’s life by selecting him for Project Rebirth and injecting him with the serum. The scientist is killed by an undercover HYDRA agent, but his work lives on with Captain America, and now "What If…?’" via Captain Carter.

Both Steve and Peggy run towards the grenade in "The First Avenger"

Peggy and Steve run towards a grenade

Peggy and Steve are similar people. Perhaps this is what draws them together and makes them one of the MCU’s best couples; they’re both brave, selfless and strong. They understand what it’s like to be an underdog: Peggy fights against sexism throughout her life, while pre-serum Steve was beaten up and bullied for his small stature. People constantly underestimate them. "The First Avenger" and "What If…?" explore the hardships they face; even after taking super soldier serum, they’re both still treated as outcasts by their superiors in the military.

Other people’s perceptions aren’t the only thing that unite them, however. During "The First Avenger," Colonel Chester Phillips (Tommy Lee Jones) surprises the Project Rebirth candidates with a test of character, by throwing a "live grenade" towards the soldiers. While the rest flee, Steve jumps on the grenade, showcasing his selfless determination to protect other people. This is a key moment for Steve; Dr. Erskine resolves that Steve is the perfect candidate for the super soldier serum, leading to Steve becoming Captain America.

Steve isn’t the only person to run towards danger instead of fleeing from it. In the same scene, Peggy can also be seen running at the grenade. This connects Captain America and Captain Carter as worthy super soldiers — and good, selfless people.

Hayley Atwell didn’t expect to reprise her role as Peggy Carter

Hayley Atwell as Peggy Carter

Peggy Carter broke boundaries both on-and-off the big screen. While the character spearheaded S.H.I.E.L.D, she also proved to be a surprise hit with fans thanks to her role in "Captain America: The First Avenger." Actor Hayley Atwell revealed in an interview with Den Of Geek that she "had no expectations" of continuing Peggy’s story in the MCU after "The First Avenger." Peggy proved too popular with fans to shelve, however, and soon made her way to the small-screen for ABC’s "Agent Carter."

"I think it’s the popularity of the character," Atwell explained. "We really enjoy working together — myself and the Marvel team — and so, I think it was based on that, and based on the response that the fans were giving, the feedback … I think people wanted to see more of her."

Atwell has played Peggy in other MCU installments set after "The First Avenger." Steve visits an elderly Peggy during "Captain America: The Winter Soldier," and attends her funeral (sob) in "Captain America: Civil War." Peggy also appears as the Director of S.H.I.E.L.D. in "Avengers: Endgame" and "Ant-Man," as well as showing up briefly in Steve’s Wanda-induced hallucination in "Avengers: Age Of Ultron." "What If…?" takes Peggy on a different journey as Captain Carter. Will Atwell get to play super soldier Peggy in live-action? With multiverse madness on Marvel’s horizon, anything feels possible.

Peggy isn’t the only "Agent Carter" alum to appear in "Avengers: Endgame"

Peggy Carter and Edwin Jarvis

Peggy is one of the many Marvel characters to appear briefly in 2019’s "Avengers: Endgame." After their botched first attempt to steal the Tesseract in 2021, Steve Rogers and Tony Stark use their remaining Pym Particles to travel to 1970. The two infiltrate Camp Lehigh, the US Army facility where Steve initially trained, and manage to successfully swipe the Space Stone, as well as some more Pym Particles. Cap and Iron Man also share an emotional reunion with a lost loved one: Tony with his father Howard, and Steve with Peggy.

Another "Agent Carter" alum appears alongside Howard Stark as he says goodbye to Tony. James D’Arcy portrays Edwin Jarvis, Howard’s butler and friend. Jarvis played a prominent role in "Agent Carter" as a sidekick to Peggy in her adventures. Eventually, Jarvis would go on to inspire Tony Stark’s A.I, which Tony transfers into Vision’s body during "Avengers: Age Of Ultron."

Peggy has a husband — and it isn’t Steve…

Peggy Carter and Daniel Sousa

In her "Captain America: The Winter Soldier" cameo, Peggy credits Steve for bringing her and her husband together. "Agent Carter" suggests that her husband is Agent Daniel Sousa, a former US Army officer portrayed by Enver Gjokaj. Like Steve, Sousa fought in World War II, as a United States Army officer. Tragedy cut his tenure on the front lines short, however, when Sousa lost a leg during battle. After that, the veteran worked for the SSR, like Peggy, who he reunited during "Agent Carter."

The ABC series isn’t clear whether or not Peggy married Sousa, or whether he is the father of her two children, also mentioned in "The Winter Soldier." With the multiverse madness kicking off in the MCU thanks to Sylvie in "Loki," it’s possible Steve could actually be Peggy’s husband — in an alternate timeline. Cap returned to the past in "Avengers: Endgame" to reunite with his lost love. His actions could have created a divergence in the timeline, and another variant of Peggy Carter.

She’s not Cap’s best girl in the comics

Sharon Carter shares a moment with Steve

Peggy might be Steve’s best girl in the MCU, but in the comics, Steve’s main love interest is a different Carter. Sharon Carter (Emily Van Camp) made her MCU debut during "The Winter Soldier" as S.H.I.E.L.D.’s Agent 13, before reprising her role for "Captain America: Civil War" and "The Falcon And The Winter Soldier." Sharon and Steve never managed to capture their chemistry from the comics in the MCU; partly due to the discomfort of seeing Steve kiss Peggy’s niece, and partly due to the lack of development given to exploring their relationship on the big screen.

In the comics, Sharon has long been Steve’s primary love interest. The character debuted in 1966’s "Tales Of Suspense" #75. Crossing paths with Captain America soon after he is revived from the ice, Sharon accompanies Steve on various missions. The two fall in love — although, like any good comic book couple, it isn’t long before their dual lives threaten to tear them apart.

Peggy also debuts in "Tales Of Suspense" during flashbacks to Steve’s origin story in World War II. Peggy’s exploits as a freedom fighter inspire Sharon, her niece, and she has a minor role as a supporting character in various Captain America comics. When it comes to Steve’s heart, however, there’s no doubt that it belongs to Sharon — in the comics, anyway. Peggy is more of a passing love interest, similar to Sharon’s role in the MCU.

Peggy was 95 when she died

Peggy Carter's funeral

During "Captain America: Civil War," Peggy Carter passed away peacefully at the age of 95. Steve attends her funeral, as does Sharon Carter, her niece. Sharon’s eulogy is a rousing send-off for such a trailblazing character. Sharon recounts how Peggy dealt with the discrimination she faced working in espionage as a woman during an era of heightened sexism and gender roles: "Compromise where you can. Where you can’t, don’t." Even in death, Peggy’s words continue to inspire Steve during his "Civil War" dilemma, solidifying his resolve to not sign the Sokovia Accords.

Peggy herself tells Steve in "The Winter Soldier" that she lived a full, rich life. Her accomplishments include founding S.H.I.E.L.D., paving the way for women’s rights, and working to dismantle tyrannical regimes like HYDRA. One thing is clear; Peggy was always destined to change the world, regardless of whether she donned the shield and super soldier serum as Captain Carter.

She helped clear Howard Stark’s name

Peggy’s friendship with Howard Stark is established in "The First Avenger," as well as the Disney+ series "What If…?" "Agent Carter" also explores their relationship, with Peggy helping to clear the senior Stark’s name when he is accused of betraying his country. Howard reaches out to Peggy and insists he is being framed for selling his weapons to overseas buyers. Peggy uses the opportunity to clear her friend’s name — and prove a point to her sexist co-workers at the SSR.

Peggy and Howard share a lifelong friendship throughout the MCU. Together, they helped found S.H.I.E.L.D. (which, admittedly, doesn’t go too well, considering that HYDRA infiltration and all… ) so it’s within the realm of plausibility that Peggy could have played a part in Tony Stark’s childhood. Pioneering Aunt Peggy could have inspired a young Iron Man, as she inspired her niece, Sharon, to become a S.H.I.E.L.D agent.

Peggy Carter was the first female character to lead her own MCU project

Thought Captain Marvel was the first female character to star in a solo project in the MCU? Think again. Long before the release of "Captain Marvel" in 2019 and "Black Widow" in 2021, Peggy spearheaded the ABC series "Agent Carter," as well as the Marvel One-Shot that effectively served as its pilot. If Steve is the First Avenger, then Peggy is the MCU’s First Lady, surpassing Marvel titans like Captain Marvel, the Wasp and the Scarlet Witch to appear front and center in her own MCU project.

Peggy had largely been a supporting character pre-Phase 4, but with the debut of her shield-wielding variant in "What If… ?" everything could change. If Captain Carter does show up in live-action during "Doctor Strange in the Multiverse of Madness," then it’s possible she could eventually lead to her own solo film in the MCU. Like Steve Rogers and Sam Wilson, Peggy makes a perfect Cap — and fans have only seen the tip of the iceberg when it comes to her story.