Cat People used to be ordinary cats. A mage named Ebrok used his powers to transform them into more intelligent and with humanoid appearance people. Cat People then started to multiply naturally. Then over time they started to grow even more intelligent, eventually they rebelled, but lost that battle. Other magicians didn't trust them anymore and banished them to "Land Within". This dimension turned out to be Hell, at first they were in disarray, and fought each other. But they still grew in intelligence; eventually they created treaties and stopped all wars between themselves. Then in unified effort they used their knowledge in magic to create an artificial sun. Small part of hell was transformed as their own, and renamed as Land Within. They just wanted to live their lives and now cut off from humans they had that chance. They chose a representative from each generation called Balkatar, it was more of an title than a name. Balkatar's job was to answer magician summons and do their bidding.
However Ebrok had kept few Cat People hidden on Earth and they worked together in secret. Other magicians found out and killed Ebrok, enraged the cat people tossed one of the weapons at the assailants, it was how Black Plague started to spread. It was not the Cat People intent however, and they retreated to mountains and started to work on the cure. Still the magicians tried to kill them, and they summoned Balkatar to protect themselves, he was no help as he had promised to help magicians. Having survived the battle the Cat People tried to create more of themselves from cats, but failed. Then they discovered magic to fuse humans with cat souls their first creation was named Tigra, she was a chosen warrior for them. She destroyed the magicians and Cat People could work on the cure for the Black Plague undisturbed and they succeeded. Now Balkatar had a new function and he was summoned by the Cat People to mate with Tigra. A new generation of Cat people were born from that union, and they decided to stay on Earth. Dr. Joanne Tumolo was descendant of these Cat People.
Over time Cat People were able to create a cure for every illness, and that created a problem, they were overcrowding their land in Land Within. They still answered magician summons; one called Daemond was such a mage. He ordered Balkatar to kill Morbius, and he of course obeyed. King Gerark, had a telepathic link to Balkatar and he found out about the creature, and devised a plan. He ordered Balkatar to bring Morbius back to Land Within, even if it meant to disobey the mage. Balkatar followed his king's orders and accepted that for disobeying the mages wishes, he was to be put to death, as it was the law. King Gerark then told Morbius of their overpopulation problem, and that he was their solution. He was to be let loose and he would satisfy his thirst on Cat People. Morbius tried to resist, but the thirst won, he was seen and a mob captured him. Morbius was thrown into the river, and the current pulled him away from the Land Within. Cat People were left to fight their own problem.
At the beginning some of the Cat People had fled from hell dimension and came to earth. They led their lives secretly and posed as humans. When a young woman named Greer Grant sacrificed herself to save one of them, the Cat People offered Greer a chance to save her life, but that meant to be transformed into one of them. She agreed to these terms and Tigra was created anew. Tigra then stayed with them as one of them.
There was one of the Cat People named Tabur, he was not originally Cat People but a creation of High Evolutionary; he was taken in by Cat People of Earth when he alone was left behind when High Evolutionary left Earth. Tabur used one of Cat People's inventions and tried to conquer the Earth. Earth bound Cat People revealed themselves to the humans and fought against Tabur. The danger was averted, and Cat People were ahead for rough times. Tigra helped them as she could, but was not able to prevent them all dying.
When Tigra had troubles with her cat-form, as she was turning more feline by the moments. She sought help, and one of the helpers turned out to be Morbius, he taught them the Balkatar summoning ritual. All of West Coast Avengers used that ritual, and Balkatar teleported them to Land Within. At first Cat People captured them, but when they found out that Tigra is with them, they granted her the audience with the king. But Tigra wanted to halt her feline transformation, and the king offered her a deal; she would have to kill Master Pandemonium and they grant her wish. Tigra accepted it without West Coast Avengers knowing and afterwards they spent a little time with the Cat People celebrating.
A little time later, Tigra and Hank Pym were kidnapped by Allatou, and West Coast Avengers traveled to hell to free them. They were successful on freeing their friends but were trapped in a boat on River of Death, Master Pandemonium was trapped along with them. It took them three days, but they reached a shore, the shore of Land Within. Cat People imprisoned Master Pandemonium, and offered Tigra the chance to kill him. Tigra refused however and was stripped of the Tigra's cat soul reverting her back to Greer Nelson. Cat People then imprisoned all of West Coast Avengers and their allies. But them being heroes, they soon escaped, in a fight Tigra's soul was released and it again bonded with Greer, this time even stronger than before, even Granting Greer a cat's tail. Seeing that, Cat People believed her to be real incarnation of the first Tigra. Cat People decided to let her and her friends to leave Land Within.
Fantastic Four happened on the Land Within while exploring underground caverns. They didn't get the warm welcome as Thing remembered from the first visit with the West Coast Avengers. And it was revealed that the Cat People worship Belasco, who was one of the old magicians who exiled them to Hell. Fantastic Four managed to escape the Cat People by River of Death.
Somehow Tabur found about the other Cat People living in hell and sought a way to get there. He eventually managed to find his way there, and challenged king in a fight. Tabur won and was selected as a new king and new Balkatar. Heeding a call from Agatha Harkness, Tabur came to Earth, seeing injured Tigra who had reverted more cat-like in time. Tabur changed her back to her humanoid form, still with striped fur and tail though. He then wanted Tigra to be his mate, to legitimize his rule. Tigra refused and they fought, Tabur was defeated and reverted into a house cat.
It appears that some Cat People on earth are still around, as Tigra got one of their old safe houses to use for a base for Avengers Resistance. Tigra once more sought them out when she was pregnant and gave birth to baby boy she named William Nelson. She let Cat People watch over her son, until it's safe enough to be reunited with him.