Mr. Wu is a slug-like alien and the owner of a Chinese restaurant in Men in Black 3.
Kay and Jay go to investigate his restaraunt after Kay receives a phone call from new Men In Black chief Agent O, reporting a non-earthly disease from his patrons. Mr. Wu, putting on a fake accent, tries to stall them, first by warmly greeting them and offers them a table, then pretending to not know what they are talking about when they demand to see his tanks in his back kitchen. After some prodding from Jay, Wu drops the accent and is forced to bring them to the kitchen, where they notice many health violations of unlicensed alien fish. One of them involves a Spikey Bulba, which seemingly disturbs Kay. Wu insists that the fish is of Earthly origins, but Kay ignores him, snatching off his hat and apron, revealing his true sluggish alien appearance and starts demanding to know who the Spikey Bulba is for, going even as far as to start hitting him in the face with it. However, Wu only stubbornly insists that the Bulba is for nobody in particular, and is just kept around in case anybody wants it. Jay eventually intervenes and reminds Wu of their agreement that only humans be fed fish from no other world except Earth. Wu attempts to make amends by serving them their "favorite noodles," to which they reply in disgust, as they have a clear distaste for his noodles. Nonetheless, Kay orders them anyway, and admits they are not too bad.
After Kay realizes that assassins are posing as common patrons and that his old time nemesis, Boris The Animal, has escaped from prison and is planning his revenge, as well as to reveal his taste for Spikey Bulba. After killing all of the assassins, Kay goes into the kitchen and gets into a confrontation with one of Wu's chefs, only for Kay to kill him when he repeatedly bashes his head in with a pan. He then turns around to see Wu's dead body pinned to the wall, as well as seeing a shadow and hearing a growl going up the stairs.
However, with the 1969 timeline altered, with Boris now dead, it is presumed that Wu is still alive and was taken into custody for his actions.