Pappachi is Estha and Rahel's grandfather, Ammu's father. He was once an Imperial Entomologist, which is a frou-frou way of saying that he studied bugs for the government. His biggest failure in life came from his biggest triumph: he discovered a rare breed of moth, but he didn't get credit or even naming rights for his discovery. Pappachi was an angry, jealous man who beat Mammachi regularly. He dies before the action of the novel really kicks off, so he's referred to mostly as a memory.