Walter Bertram Potter (1872-1918), known as Bertram, was the younger brother of the children's author and illustrator Beatrix Potter. As a child he shared his sister's passions for drawing and natural history and was joint custodian of a menagerie of exotic pets, including salamanders, bats, rabbits, mice, lizards, newts, snails and a frog, tortoise, owl, ring-snake, jay, jackdaw and kestrel. Both children were accustomed to boiling, dissecting, and sometimes killing animals to study their anatomy so it is possible that Bertram pickled the snake and fish himself. In 1884 Bertram even advised Beatrix how to kill and stuff a pet bat: ‘If he cannot be kept alive as I suppose he can’t, you had better kill him, & stuff him as well as you can. Be sure to take his measurements most carefully before you stuff him’.

It was Bertram who first encouraged Beatrix to publish some early rabbit drawings as greetings cards in 1890 and she continued to seek his advice when illustrating the Peter Rabbit books: 'My brother is sarcastic about the figures; what you & he take for Mr. McGregor's nose, was intended for his ear, not his nose at all' (Letter to Norman Warne, 2 May 1902). Although overshadowed by the success of his sister, Bertram became an artist in his own right. He produced much larger scale oil paintings and etchings and exhibited work at the Royal Academy.