I subbled upon this very interesting article on the origins of the idea that Jesus was an angel
The begining od the article:
The idea of pre-existence originated with PLATO and was later developed by XENOCRATES (d.314 BC). In time, the first century Middle Platonic philosopher NUMENIUS introduced the idea of a 2nd transcendental entity between the Supreme Being and the universe. This entity, subordinate to the Supreme God, was called the Demiurge – meaning maker or builder. Because matter was viewed as evil God could not have any association with it. Only the Demiurge could deal with it and so he acted as builder or agent of creation.
The concept that Jesus had acted as agent of creation because he had existed in a different form prior to birth has been believed by many since the Christian philosopher Justin Martyr first used the word pre-existence with reference to Jesus in about 150 AD. However, Justin was a believer in the idea that Socrates and Plato were inspired by God. He had been thoroughly schooled in the Greek philosophical thinking of his day, including the thoughts of Numenius whose ideas he found attractive. With his mind so receptive, Justin found it easy to apply such ideas in his interpretation of the Christian Scriptures.