Of all the friendships in the Dragon Ball franchise, few are closer or more enduring than the one between Tien Shinhan and Chiaotzu. Introduced halfway through the original Dragon Ball as new rivals for Goku and his friends, the unlikely duo are among the most visually distinct of the Z Fighters, with Tien possessing three eyes and Chiaotzu as a mythical Chinese jiangshi, or ghost, complete with unique psychic abilities.
Even in those more antagonistic early days, Tien always had a soft spot for Chiaotzu in one of the more noticeably protective dynamics in the franchise -- and one whose backstory could be based on Chiaotzu's supernatural nature.
While Chiaotzu is never described outright as a ghost in Dragon Ball, even being killed three times by conventional means over the course of the franchise -- once by King Piccolo in Dragon Ball and later by the Saiyans and Majin Buu in Dragon Ball Z -- he still maintains many traits of a jiangshi.
Throughout the sprawling story, Chiaotzu never visibly ages and maintains the same childlike appearance and demeanor, even decades later by the events of Dragon Ball Super. All the while, Tien and Chiaotzu are not only best friends who constantly train in martial arts, but Tien carefully takes care of Chiaotzu as if he were a brother.
There is no indication as to why Tien is such a close big brother figure to Chiaotzu, with the origins of their relationship never fully revealed. They were introduced as traveling conmen who preyed on small villages before being foiled by Goku. The two resurfaced as the star pupils for Master Shen's Crane School of Martial Arts, the rival to Master Roshi's Turtle School where Goku, Krillin and Yamcha trained. Tien and Chiaotzu's backstory is never explored further, with the two opening their own martial arts school together in Dragon Ball Super -- though Tien remains as protective of Chiaotzu as ever.
There is nothing to suggest Chiaotzu is directly related to Tien though. In the Japanese language iteration of Dragon Ball, Chiaotzu uses honorifics denoting older brother to Tien. This is not uncommon in Japanese culture, but shows a degree of noted respect and familiarity between the two fighters. Another possibility is that Chiaotzu is a ghost of a childhood friend or little brother to Tien. This would explain why he's so protective of Chiaotzu, even going as far as to prevent him from fighting against the Androids or participating in the Cell Games as he didn't want his good friend to get hurt.
Tien is normally a stern and stoic figure not prone to revealing his emotions, but he makes no attempt to conceal how much he cares for Chiaotzu. It was Master Shen's cruel treatment of Chiaotzu that helped inform Tien's decision to leave his old master, but the full nature of why exactly the two are so close or how they first met has yet to be revealed.
Chiaotzu is the only jiangshi seen in the Dragon Ball franchise to date, which may suggest a more tragic origin story for the ghostly fighter. Whatever the nature of their dynamic, the once-villainous Tien found a simpatico in Chiaotzu that helped steer him to the light in the most unique friendship Dragon Ball has ever seen.
