Character who could lead to a sequel?

In the early hours of Sunday morning I had an idea for a character, rather than a book. I had just had the idea for a fifth book, but worried I may not be good enough to write it given the subject and complexity of it, more of that over the next few years. Perhaps I have had my “Jack Ryan” or “Dirk Pitt” moment, as yet I have no idea as to who this character is, or what they do, I am beginning to imagine they could fit into the third novel and then I would have a base to expand the character into a sequel, prequel or series. It needs serious thought.