What is the brocken spectre?

bbc.co.uk/news/uk-scotland-highlands-islands-31447148

A spooky weather effect, which in the past was thought to be a supernatural creature, has been photographed in Glen Coe. But what is the story behind it?

The myth describes him as a Scottish Big Foot, said to loom large in shifting grey cloud on the UK’s second highest mountain.

The Big Grey Man of Ben Macdui first came to prominence in the 1920s during a dinner speech at an annual gathering of the Cairngorm Club in Aberdeen. etc .