The two natures of Jesus refers to the doctrine that the one person Jesus Christ had/has two natures, divine and human. In theology this is called the doctrine of the hypostatic union, from the Greek word hypostasis (which came to mean substantive reality). Early church figures such as Athanasius used the term "hypostatic union" to describe the teaching that these two distinct natures (divine and human) co-existed substantively and in reality in the single person of Jesus Christ. The aim was to defend the doctrine that Jesus was simultaneously truly God and truly man.