Arthur Christmas Bayer was an art critic who was a potential version of Panda.
Iris Wildthyme, looking for Panda (having lost him on a previous adventure), eventually found Bayer in Stella's in London. While he looked nothing like Panda and had no memories of Iris, she was convinced it was him and started frantically following him around.
Although he believed he wasn't Panda, he sounded and talked exactly like him and lived in the very house Panda had always dreamed of - and after Iris showed him a photo of herself and Panda, he started to remember having written stories in his youth that bore a curious resemblance to Iris' own adventures.
After declining to travel with her, he set about writing his stories properly. (AUDIO: Looking for a Friend)