I think Augustine would be an interesting candidate. John Wesley from my own denomination. Many of the early church theologians. We live with a fairly well developed system of theology and Christian belief . However, the early church had to define and articulate the faith. For this they used the methods of logical inquiry available to them based on the idea that theology had to be understandable and had to be internally consistent. So many of them used tools of logical and reason to examine the Christian faith. Were many of them rationalist in the modern sense, no but were they in their time and place yes.