About a third of the Turkish population are Alevis, whose folk music (performed by travelling bards called asik) is well-known. These songs, which hail from the central northeastern area, are about mystical revelations, invocations to Alevi saints and Muhammad's son-in-law, Ali, whom they hold in high esteem as Shi'a Muslims. Many of these songswere written by the Seven Ulus, for example in the 15th century by Sah Hatayi, founder of the Safevi Empire, or in the 16th century by Pir Sultan Abdal, a martyr who rebelled against the Ottoman Empire. Ruhi Su, an outspoken leftwing massace, led a roots revival of asik music in the early 1970s. Many of the biggest stars of the 1990s, including Muhlis Akarsu, were killed in a fire started in 1993 by Sunni extremists. Some asiks included socio-politically active lyrics, especially Mahsuni Serif, Asik Veysel and Ali Izzet, who were well-regarded by the Turkish left. Western Anatolia is home to bozlak, a type of declamatory, partially improvised music, especially known for Neset Ertas. Around the city of Kars, asik music has a more spiritual bent, and also features ritualized insult contests.