Black Panther has been a member of the Avengers for many years now, but the reason T’Challa joined the team is surprising for such a heroic character, hinting at the kind of paranoia that marks Black Panther as not just a hero, but a ruler with wider responsibilities.
Black Panther joined the Avengers not long after his first appearance in Fantastic Four #52. As revealed in a flashback sequence in Black Panther #8, after fighting side by side with Captain America and Sharon Carter, Cap asked Panther if he would join the Avengers, since a spot was open. He tells Cap he will “consider it very carefully.” We know what happens next - Panther joins the team and becomes a long-serving member in good standing. It's a long time until Captain America realizes the real reason T’Challa joined the team.
In Marvel Knights Black Panther #8, by writer Christopher Priest (Justice League), artists Joe Jusko (Vampirella) and Amanda Connor (Harley Quinn) and inker Jimmy Palmiotti (Power Girl) readers learned the true reason the Panther joined the team, and it went a long way to redefining his character. The story opens with Black Panther on a visit to New York. A friend, Senator Rakim, has organized an event that sees hundreds of thousands of African-Americans come to see the Panther, a real African king. Panther is not happy, fearing that policing conditions at the meeting could lead to violence. He also believes the people gathered are militants, and not average citizens. Unfortunately, a demonic dissident named Achebe has paid snipers to fire into the crowd, in order to actually start a riot and slur the Panther’s name. The Avengers, who had shown up to support Panther and help with crowd control, are drawn into the melee, and that’s when the Panther drops his bombshell.
Achebe goads Panther, pointing out that Panther, a black man, was always standing behind the white Avengers. He accuses Panther of selling his people out, and that is when the Panther reveals his true motivation for joining the Avengers: to spy on them and to assess their threat level, with plans to act against them if necessary. The other Avengers fighting the crowd are shocked to hear this, and after the battle, they ask him about his “bluff,” to which he replies he was not bluffing at all.
This shocking revelation about Black Panther helped begin to redefine his character. A former B-lister, the Panther’s visibility went up from there, a path that led him to the MCU, international acclaim, and his current status as one of the controlling forces (and main funding sources) behind the Avengers. Priest and his collaborators get to the heart of the Black Panther, showing him as someone who stays one step ahead of his enemies and his friends, all in the name of protecting his people.