The Green Man is an interesting figure to me as so few know who he really represents. I do think the Green Man represents our early relationship with Mother Nature herself and it not necessarily a God. I do think Pan or Dionysus evolved into the Green Man in order to survive the onslaught against Paganism by the Christian Church.
As one can see, there are many images of the Green Man and he is also seen on Churches themselves. I think that is because the churches were built on Pagan spiritual grounds and the symbol reminds the native peoples of their earlier beliefs.
The Green Man does look Celtic in nature, but also can be from any of the Old Ways. I also think he is related to Merlin and Camelot and plan on exploring that aspect some more.
I also love all the artwork that is the Green Man.