First Appearance: Tales of Suspense #75 (March 1966).
Appearances: A surprisingly large number of stories.
Years Active: 1939? to the present.
Relatively little is known about "Mademoiselle." She was Margaret "Peggy" Carter, the (much) older sister of Sharon Carter, the modern adventuress and former SHIELD agent. "Mademoiselle" was a mysterious OSS agent who fought alongside Captain America (I) during World War Two and was romantically involved with him. She was occasionally known as "Agent 13," although (confusingly enough) that was more often the codename of her sister Sharon during the modern era. (It might be argued that Peggy was the "Agent 13" who was present and active at Project: Rebirth, the operation which created Captain America.)
Peggy is somehow still alive and recently was a member of the Avengers' staff.