Xin Fu was the promoter and host of the underground earthbending tournament Earth Rumble VI. He was a proficient and powerful earthbender as he was once an active competitor of the tournament himself, but unlike most of the other wrestlers, he was also very business savvy and was always looking for another way to make money. He became stubborn and greedy to the point where he would do anything for money, even willing to make deals with the Fire Nation. He and Master Yu were later hired by Lao Beifong, Toph's father, to retrieve his daughter, who had run away from home to join the Avatar on his travels, and Xin Fu thus became a bounty hunter.
Xin Fu was the host and commentator of the popular earthbending tournament, Earth Rumble VI. When the tournament ended in a swift victory for Toph over The Boulder, he tried to make the game more interesting by offering a sack of gold pieces to anyone who could defeat "The Blind Bandit", Toph's alias. Aang took on this challenge, in order to get close enough to Toph so he could talk to her. However, the blind earthbender did not want to talk and commenced to attack Aang. While evading her attacks, the airbender accidentally knocked her out of the ring with a powerful gust. Toph's defeat without physical contact caused The Boulder to doubt the fairness of Aang's victory and he suggested that Toph purposely lost the match to Aang, and then split the money with him afterward. Xin Fu became enraged with the idea that someone had cheated him and prompted the other Earth Rumble contestants to help him take revenge. He kidnapped Aang and Toph in metal cages and left a ransom note behind, stating that he would release Toph if the Beifong's brought five hundred gold pieces to the arena.
After Lao and Master Yu paid the ransom for Toph, he released her, but announced that he was going to collect the bounty set on the Avatar's head by the Fire Nation. When Sokka and Katara prepared to fight him, the contestants of the earthbending tournament gathered around him, ready to defend him if needed. The Water Tribe siblings called upon Toph to help them out, which she did by easily dispersing herself of all the contestants except Xin Fu. The tournament host proved himself to be a powerful earthbender, as he lasted the longest against Toph, but he was still defeated by her.
When Toph later ran away from home to join Aang and his friends on their travels, he and Master Yu were recruited by Toph's father who believed Aang had kidnapped Toph. Lao instructed both men to retrieve her by "any means necessary."
After tracking their prey to the Misty Palms Oasis, it became clear that Xin Fu only cared for the money, as he stated that the bounty for retrieving Toph was paid dead-or-alive; he was, however, quickly corrected by Master Yu who stated that he was "certain Lao wanted his daughter alive". Xin Fu took notice of the town's information kiosk and the Fire Nation wanted posters it supported. After spotting the fugitives Iroh and Zuko entering the cantina, the two bounty hunters temporarily changed their targets. The cantina was filled with shady characters, so Master Yu insisted on patience to wait for the right moment, but Xin Fu's impulsiveness got the better of him and he moved to capture them. A White Lotusmember turned the whole bar against them by alerting the others of the bounty set on Iroh and Zuko's head. Xin Fu and Master Yu easily fought off all the men in the bar, but their targets managed to slip away in the confusion. After searching the whole town to no avail, they focused their attention again on capturing Toph.
In Ba Sing Se, they finally managed to catch her in a metal cage by luring her into a trap with a forged letter from her mother. Though Master Yu was the strategic mind of the duo, Xin Fu demonstrated more common sense when Toph tried to trick the two into letting her out of the box. After Toph discovered that there were still earth particles hidden in the metal, she figured out a way to bend the metal itself and thus became the first known metalbender. She freed herself out of her metal prison and turned the tables by trapping Xin Fu with Master Yu in the very same metal box in which he had imprisoned her. Much to Xin Fu's dismay, Yu immediately announced that he had to go to the bathroom. He slammed his head against the metal wall in irritation upon realizing that he would be trapped in that cage with the earthbending instructor forever.
Xin Fu originally appeared to be an enthusiastic, passionate host, seemingly enjoying his status as the head of the Earth Rumble VI tournament and even offering a monetary reward at one point. Later events, however, revealed him to be a more sinister man, who was easily angered if he believed he had been cheated. He willingly fought one of the tournament's most prominent competitors and accepted Lao Beifong's orders to escort Toph home in exchange for a large bounty. Xin Fu was a toughened man and a formidable opponent.
As a successful former competitor of the Earth Rumble Tournament, Xin Fu was a very capable earthbender. During his first demonstration, he was able to quickly launch a huge barrage of rocks. His style of combat is very direct and a sheer show of force. He is also very strong, able to hold two men up simultaneously. Likwise, he has also shown great dexterity and capable unarmed combat skills, able to kick incoming assailants while holding up the said two men.
Although partly obscured, his name in Toph's ransom letter was written as 辛富 (xīn fù) which translated as 'Bitter rich'.
Xin Fu may be a pun on a homophone of his name 幸福(xìngfú), the Chinese word for happiness or bliss. Note the similar characters common with Chinese homophones 辛(bitterness and hardship) and 幸(luck), as well as 富("fortune" as in "wealth") and 福("fortune" as in "blessed with happiness").