This is a Brocken Spectre with the hills of the Scottish Borders in the background.
A Broken spectre is a phenomenon which occurs when your own shadow is cast onto cloud or mist. The spectre can only ever be seen by the owner of it.
This one is very rare as the view is fully visible. The only other ones I have ever seen (photos included) have been in mountains with the spectre cast onto a sea of cloud which completely obscures anything else from view.