Origin of the Trinity

I found an interesting tidbit, while reading Karen Armstrong's book, "The Case for God". It almost sounds like she is saying that the doctrine of the trinity was actually something that originally came from the stoics. I know that incarnation of God's and the death and resurrection of a God are important elements in mythology. So much so that early Christian apologists accused Satan of planting these stories into pagan religions because he knew what was coming next and he wanted to discredit God and Christianity. But was the Trinity also an existing concept before Christ? Karen Armstrong writes:

Stoics also discovered that meditating on the immensity of the cosmos revealed the utter insignificance of human affairs, and that this gave them a saner perspective. They saw the whole of reality as animated by a fiery vaporous breath that Zeno called Logos ("Reason"), Pneuma ("Spirit") and God. Instead of railing against his fate, the philosopher must align his life to this Spirit and surrender his entire being to the inexorable world process. Thus he himself would become an embodiment of Logos.

Now when I read this, the first thing I thought was Gospel of John. After all John is obsessed with Logos ("In the beginning was the word (Logos) ..") and he also probably spends the most time of any Gospel discussing the Spirit. Most of the texts that support the Trinity come from John and there is evidence that some scribes added language to make the case stronger (See Bart Ehrman's book for more details.) Was the writer of John influenced by stoicism so that he used metaphors from the Greeks to describe Jesus? Are we correctly understanding what the author of John intended? Or has our interpretation been corrupted by our Western tradition, which has incorporated much from Greek thought? Or is Karen Armstrong overstating the similarity? Afterall she has put a huge amount of effort into finding the similarities between religions. Anyway it looks like it might be worth my while to find out exactly what the Stoics believed.