https://screenrant.com/captain-america-peggy-carter-secret-history-marvel-comics/

Warning! Spoilers for Captain America #25 below!

Peggy Carter has been a confidante and partner of Captain America since World War II, and now Marvel has revealed her secret history. In Captain America #25 by writer Ta-Neshi Coates (Black Panther), artist Leonard Kirk (Batman), and colorist Matt Milla (X-Men Blue), readers learn just how Peggy got caught up with Captain America and the world of espionage - through a clandestine organization called The Daughters of Liberty.

Despite being Captain America’s wartime love interest, Peggy did not appear for the first time until 1966’s Tales of Suspense #77. From there, she would join SHIELD and share many adventures with not only Captain America but the Avengers as well. Peggy would die but was later reborn. In addition to being a major presence in the comics, the character has jumped to other media as well, portrayed by Hayley Atwell in both Captain America: The First Avenger and the Agent Carter television show. During Coates’ run on Captain America, a number of surprising revelations about Carter were made, including her leadership of The Daughters of Liberty, an underground group consisting of women dedicated to the cause of liberty and justice.