The White Ox True Form is the Bull Demon King’s own revealed body in Journey to the West. It is neither his mount nor a separate animal companion, but another bodily form of the same character during a contest of transformations.
Chapter 61 describes him revealing himself as an enormous white ox. Exaggerated scale, horns, and physical strength establish his imposing presence. He attacks with his horns and tail while Sun Wukong changes in response and continues the struggle.
This form connects the Bull Demon King’s name with his bodily identity and carries the contest beyond ordinary weapon fighting. Its essential meaning is the same character appearing as a gigantic white ox; it introduces no separate beast into the story.