Two faithful sidekicks become leads in “The Falcon and the Winter Soldier,” a new superhero series premiering Friday on Disney+. This show takes place some time after “Avengers: Endgame,” when the newly retired super-soldier Steve Rogers (Chris Evans) announces his retirement as the patriotic hero Captain America. Rogers also gives his red, white and blue Vibranium metal shield to Sam Wilson (Anthony Mackie), a retired Air Force veteran who as “The Falcon” flies around with a jet-powered winged harness.

Wilson previously fought alongside Rogers as a member of the Avengers in other Marvel Cinematic Universe movies like “Captain America: Civil War” and “Avengers: Infinity War.” But in “Endgame,” Wilson seems reluctant to accept the role of Captain America, which might explain why “The Falcon and the Winter Soldier” isn’t titled “Captain America and the Winter Soldier.”

Wilson’s implied promotion is, however, supported by Bucky Barnes (Sebastian Stan), Rogers’s childhood best friend and World War II sidekick. Throughout most of the M.C.U. movies, Barnes and Rogers have not biologically aged since the 1940s — both men were frozen alive, though under very different circumstances, and then revived by super scientists decades later. Rogers was resuscitated by the American spy agency S.H.I.E.L.D. in “Captain America: The First Avenger,” while Barnes was both preserved and awakened by the ex-Nazi terrorists Hydra, as we see in a flashback during “Captain America: The Winter Soldier.”

Barnes and Wilson also have a complicated relationship, though they have never really been rivals. To help better understand the frenemy tension that unites them, here are some of the key moments from the comics and movies that have led up to “The Falcon and the Winter Soldier.” Major spoilers follow.

The Rebirth of Bucky Barnes

In “The First Avenger,” Barnes and Rogers fight the Nazis during World War II but are separated in 1943 after Barnes falls off a moving train while pursuing the Nazi scientist Arnim Zola (Toby Jones). He survives the fall but loses his left arm. It’s revealed later in “The Winter Soldier” that Zola, working for Hydra, captured Barnes and replaced his missing arm with a robotic prosthetic. Barnes’s abduction and revival are briefly shown through flashbacks in “The Winter Soldier” and “Civil War.”

Hydra renames Barnes “the Winter Soldier,” and trains him as a political assassin. In “Civil War,” we learn that Barnes is responsible for the murder of the weapons contractor Howard Stark (John Slattery) and his wife, Maria (Hope Davis) — the parents of the reformed industrialist Tony Stark, who fights crime as Iron Man (Robert Downey Jr.).

As we see in a flashback at the start of “Civil War,” Barnes killed Tony’s parents in 1991 after Hydra’s Russian scientists revived him in a Siberian lab. Hydra, led by the stoic Vasily Karpov (Gene Farber), influences Barnes’s actions using posthypnotically suggestive catchphrases.

Karpov’s book of mind-controlling code words is stolen later in “Civil War” by the fellow Hydra agent Helmut Zemo (Daniel Brühl). Zemo uses Karpov’s book to make Barnes fight Rogers and the other members of the Avengers, including Wilson.

Sam Wilson and the Search for the Winter Soldier

Barnes and Wilson’s relationship has been uneasy in the M.C.U. movies. Wilson is introduced in “The Winter Soldier,” the film in which we learn that Barnes survived World War II and is now a Hydra agent. The pivotal moment comes when Rogers is attacked by the Winter Soldier, whom he recognizes as Barnes, his old friend and partner.

Rogers and Wilson meet at the start of the movie, while jogging in Washington D.C., and then bond later at a local Veterans Association facility, where Wilson gives advice and leads group therapy for vets with post-traumatic stress. Wilson tells Rogers that he lost his partner Riley (Ron Underdahl) during a nighttime rescue mission in Afghanistan. He then joins Rogers in tracking and confronting Barnes in both “The Winter Soldier” and “Civil War.” Wilson also joins the Avengers some time between “The Winter Soldier” and the next Avengers film, “Age of Ultron.”