Zhang Guolao is the one member of the group whose image is instantly identifiable and slightly absurd: a very old man riding a white mule while facing its tail. The explanation offered is that the mule travels enormous distances in a day, tens of thousands of li, and that when the journey is over he folds it flat like a sheet of paper and puts it away in his wallet, then sprinkles it with water from his mouth to bring it back. Nobody in the tradition treats the backwards riding as needing further justification, and the usual gloss is that looking behind rather than ahead is the correct posture for someone who has seen enough.
His instrument is the fish drum, a length of bamboo closed at one end and struck or beaten with two rods, an instrument associated with itinerant storytellers, and he is patron of that trade.
Unlike most of the group he is anchored to something documented. The Tang official histories record a recluse called Zhang Guo who was summoned to the court by the emperor Xuanzong in the eighth century, was questioned about his age and the means of his longevity, declined honours and returned to the mountains. That is a plain record of an unusual man. The immortal Zhang Guolao, with the folding mule and the great age, is what the tradition made of him afterwards, and the atlas records the two layers separately.