That would be a picture of Neil Gaiman cosplaying as Badger from The Wind in the Willows which was one of his favorite characters as a child. It’s all part of a project by photographer Cambridge Jones who convinced a group of authors to cosplay their childhood favorites. The series of photographs is part of an exhibit at The Story Museum in Oxford.
There are 26 different authors featured including Terry Jones as Rupert the Bear, Philip Pullman as Long John Silver, Anthony Horowitz as Jekyll and Hyde, and Terry Pratchett as Just William. You can see more pictures from the exhibit over at BBC News.