Ibn Kullab was a man from a long time ago who lived in a place called Persia, which is now Iran. People used to look up to him and think he was very smart because he knew a lot about religion, which is what people believed in back then.
Ibn Kullab believed in something called "theological speculation", which is like trying to figure out what God is thinking or what God is like. He wrote many books about this and other religious topics, and people would read his books and try to learn from them.
Some people disagreed with Ibn Kullab and said he was wrong. They thought that instead of trying to guess what God was like, people should just believe what their holy book said and not try to understand it too much.
Eventually, many people stopped following Ibn Kullab's ideas and they became less popular. But some people still think he had some good ideas and they study his work today.