Man of Nias, Sumatra, Indonesia in ceremonial costume. Mentawai (also known as Mentawei and Mentawi) people are the native people of the Mentawai Islands, West Sumatra province, Indonesia. The Mentawai population is estimated to be about 64,000. The Mentawai language belongs to the Austronesian language family. The people are characterised by their heavy spirituality, body art and their tendency to sharpen their teeth, a practice they feel makes one beautiful.