He may be the pilot's version of the Scarecrow, although since Dorothy's adventures took place in the backstory of the show, there may be another version of the Scarecrow in the show.
Jansen was a pilot in World War II, whose callsign was Scarecrow. He was sucked into the Land of Oz.
Due to the strange effects of Time in Oz, he arrived in Oz the same time as Alexandra Wilder, who originated from a much later era than him. He began to travel with her, and eventually joined her quest to free Ozma. (Lost in Oz)