The John Bull Porter is a character in Mystery Train. The porter is supposed to look just like your Poptropican but with a blue hat and suit. He/She doesn't want to help you at all while you're trying to find the thief.
When you ask them what drinks the passengers ordered, he/she refuses to answer and tears off the page of their notebook containing the information and tosses it out of the window. After this, when the Coal Man is accused of committing the crime, the porter proves his innocence. He/She doesn't help much after this though they do turn up when the thief is "revealed" to be Nikola Tesla and asks you to give the Motion Capture Device to Thomas Edison. At one point you must also disguise yourself as them to sneak into Nikola Tesla's room.
The porter is the second character in Poptropica that is designed to resemble your Poptropican no matter what how you change your looks. The first is your future self in Time Tangled Island.