In Avengers #52, Roy Thomas and John Buscema had Black Panther, who had just fought alongside Captain America in Tales of Suspense, save the entire Avengers team from Grim Reaper—which led to the team asking him to sign on. He accepted the invite, and stayed with the team—relinquishing his role as King of Wakanda in the process. He’s basically a series regular from then all the way to #118. I’m not going to go over all these appearances because they don’t really progress him as a character. He’s on a team, so it’s not about his own persona or mythos.
But he wasn’t exclusive to the team. In addition to those adventures, he appeared as a pall-bearer in the first “death of Captain America” story (Captain America #113); formed a relationship and appeared with Daredevil (Daredevil #56, 69, 99); and even joined Sub Mariner for an adventure in Sub Mariner #35. Oh, and there was a cool solo story in Astonishing Tales #6-7 where he fought Dr. Doom.
What’s notable here is that he fights Dr. Doom and uses a gun for the first time (and one of the only times). It also marked the first appearance of Mockbird (known then only as Bobbie Morse), and the first time we got to see Gene Colan draw Black Panther, which was great to behold. It also led into a Ka-Zar story in Astonishing Tales #8, which was Gerry Conway’s first script for Marvel! (Panther also appeared in Ka-Zar #1.)
From there, it was on to Fantastic Four #119, in which he takes the unfortunate name of Black Leopard—a decision of Marvel editorial, made to sidestep any implication that he was associated with the black militant party that was active at the time. It’s notable but irrelevant that that was also the first appearance of HERBIE the robot.
There are a smattering of other appearances in this time period, but that basically brings us to late 1973, when things really changed for the character and for the first time since his first appearance in Fantastic Four #52 back in 1966 the character gets a real distinctive personality.
Next: Panther gets his own book!