No he isn't, he just helps them in infinity war

no he is one

you should all ready know this

Comics, yes. He's a long time Avenger. Not always, it's on and off, but he's been an Avengers for a looooong time.

Marvel Cinematic Universe, not yet.

In the comics, yes. As of the recent issue, he is the new leader of the team.

No I don’t Believe so