Brother Sum is the main antagonist of the 2004 action-comedy movie Kung Fu Hustle.
Brother Sum was the leader of a gang known as the Axe Gang, and his gang had killed off all the other mob bosses and gangs in Shanghai. Sum preferred to let his henchmen do the dirty work with him finishing the job. People were only allowed to live peacefully in some areas that the Axe Gang didn't bother entering. This changed when two trouble-makers, Sing and Bone, arrived in Pig Sty Alley, pretending to be Axe Gang members.
Sing and Bone aspired to be criminals due to their belief that heroes never win because of a rough incident trying to be good, and now decided to pick on the residents of Pig Sty Alley, but the people proved very strong and the duo chose not to fight them just by seeing them. Eventually, Sing tried to call the Axe Gang but ended up burning one member's head. After the member tried to kill a random citizen, his back was broken by a kung fu master, The Coolie. The axe gang called Brother Sum, who actually smirked when he saw his fellow gang member in pain before asking who did it, threatening to burn a mother and son if they didn't tell. When no one answered, he tried to burn them, but The Coolie admitted to what he did, and Sum had his gang attack him, but they were beaten back by Coolie and two other kung fu masters, Donut and Tailor.
After the incident, Brother Sum tried to have Sing and Bone killed via throwing axes, but they escaped their bonds before the axes hit them. Impressed, Sing told them they could be part of their gang if they killed someone. Unfortunately for the duo, they were terrible at this and ended up injuring themselves more than their victims. At the same time, Sum hired The Harpists to kill the three masters. They succeeded at this, but they recieved a beatdown from the Landlady and Landlord in response, and the Landlady threatened Sum. Sum wasn't done yet, and hired an old man named The Beast to kill the two. The Beast proved more capable than he appeared, and nearly defeated the two, but was defeated when the Landlady used the giant bell as a microphone and yelled into it. The Beast feigned defeat and attacked again, and the three ended up locked together. Sum ordered Sing to finish them off, but Sing hit him with a table leg and then attacked the east with it.
Infuriated, the Beast beat Sing to a pulp, but this allowed the Landlady and Landlord to recover and rescue Sing. Brother Sum berated the Beast, who got angered and killed Sum by punching him in the face with enough force to cause his head to spin around.