They called for me.
That is all I really know.
They called for me and I went to them. I could not do otherwise. The will of the whole of humanity was a strong thing. It smashed through the ties of time and the chains of space and dragged me to itself.
Why was I chosen? I still do not know, though they thought they had told me. And now it is done and I am here. I shall always be here and if, as wise men tell me, time is cyclic, then I shall one day return to the part of the cycle I left and which I knew as the twentieth century A.D. in the Age of Men, for (it was no doing or wish of mine) I am immortal.