Cao Guojiu is the thinnest of the eight in the literature, and the reason is that he arrived late. Groupings of transcendents circulated for centuries before the standard set existed, and the membership was not stable: different Tang and Song lists include figures who are now outside the group and omit some who are now inside it. What produced the fixed eight was the stage. The zaju drama of the Yuan period returned to them repeatedly, and by the time the Ming novel of the journey to the east was written, the membership had settled into the list used ever since.
The number itself carried weight before the members did. Eight is the number of the trigrams, of the directions, of the divisions of the year, and a group of eight anything reads as complete in Chinese arrangement. A set of eight immortals is therefore not merely eight individuals but a full compass of ways to reach the same end, which is exactly how the tradition presents them: a general, a scholar, an old recluse, a musician, a courtier, a beggar, a singer of unfixed gender and a young woman, covering rank, age, sex and condition between them.
His attributes reflect the late arrival. He is shown sometimes with a jade tablet of court audience and sometimes with a pair of castanets, and the two are not easily reconciled. He is patron of actors and of theatrical troupes, plausibly because a figure in court dress on stage was the natural candidate for the profession to adopt.