Here is a helpful guide clarifying who each person is, along with the likely reason their names are connected. Who he is: The quintessential heroic firefighter and leader of Truck 81 at Firehouse 51. Played by: Jesse Spencer Show: Chicago Fire (NBC)
It seems there might be a slight confusion in the name combination you’re looking for. and John Magnum are characters from two different, very popular TV universes. Matt Casey John Magnum