When Jack Kirby returned to Marvel, he made many covers, both for characters he had created and titles he had not. Kirby had little interest in going back to the titles that had established his fame. He returned to Captain America but he had created that title with Joe Simon, not with Stan Lee. When he took over he ignored all the work done by Steve Englehart. He kept the Falcon and Leila Taylor but otherwise he changed that title. It was not apparent to readers of that time, but Kirby was not doing super-heroes. Actually he had stopped by 1965. After the wedding in FF Annual 3 and the battle versus the Frightful Four, he took the Fantastic Four in a new direction where the strip was to achieve greatness. Gone were the mundane supervillains. Instead the quartet faced technological and extraterrestrial threats. They were adventurers.
When Kirby made new Captain America stories, the title character didn't face the typical super-villains, he faced royalists, grotesque puritans, a South American dictatorship and big business. Later in the run he faced the Red Skull and Magneto in an Annual. This is when he seems to have lost interest for he left the strip.
His return to Marvel may be more remarkable for his new titles: Eternals (similar to his New Gods), 2001, A Space Odyssey, Devil Dinosaur.
His return to Black Panther is more of a surprise. He had co-created the character in Fantastic Four and Don McGregor had made the character able to sustain his own title. Yet as in Captain America, Kirby would ignore the new ground created.
He created an adventure strip that feels closer in tone to Raiders of the Lost Ark than anything else. But he did it before Lucas and Spielberg since he did it in late 1976. Contrary to Captain America, he had room for creating new supporting characters. He created Mister Little and Princess Zanda, two members of a club of fanatic collectors. Then he returned the character to his country of Wakanda and created the regent and the black musketeers, newly introduced members of the royal family. The creation of supporting characters is necessary to the success of any strip. The threats are typical pulp stuff: menaces from the past and the future, gangsters, a would-be dictator and an evil scientist that their disregard for humanity turn into monsters .