You see, in 1965, there was a bit of a superhero boom period, with a number of comic book companies debuting their own superhero groups of titles, including Archie Comics and M.F. Enterprises. Marvel, too, wanted to expand their superhero lines. However, in the end, they were constrained by the distribution deal they were under where their chief competitor, DC Comics, kept their line of comics artificially low
In 1968, Marvel finally broke out of that deal, but they first tried in 1965, when all the other companies were debuting their superhero lines.
When Marvel thought that they had a chance at having more new comics, two of the new titles were going to be the Inhumans and Black Panther (originally called Coal Tiger).
When DC wouldn’t allow them to alter their deal, Kirby and Lee were forced instead to just have the characters debut in the pages of Fantastic Four instead, and therefore, the Black Panther debuted in Fantastic Four #52 instead…
Here is Kirby’s initial take on the Black Panther, back when he was called
Coal Tiger…