The Armenian Genocide caused widespread emigration that led to the settlement of Armenians in various countries in the world. Armenians kept to their traditions and certain diasporans rose to fame with their music. In the post-Genocide Armenian community of the United States, the so-called "kef" style Armenian dance music, using Armenian and Middle Eastern folk instruments (often electrified/amplified) and some western instruments, was popular. This style preserved the folk songs and dances of Western Armenia, and many artists also played the contemporary popular songs of Turkey and other Middle Eastern countries from which the Armenians emigrated. Richard Hagopian is perhaps the most famous artist of the traditional "kef" style and the Vosbikian Band was notable in the 40s and 50s for developing their own style of "kef music" heavily influenced by the popular American Big Band Jazz of the time. Later, stemming from the Middle Eastern Armenian diaspora and influenced by Continental European (especially French) pop music, the Armenian pop music genre grew to fame in the 60s and 70s with artists such as Adiss Harmandian and Harout Pamboukjian performing to the Armenian diaspora and Armenia. Also with artists such as Sirusho, performing pop music combined with Armenian folk music in today's entertainment industry. Other Armenian diasporans that rose to fame in classical or international music circles are world-renowned French-Armenian singer and composer Charles Aznavour, pianist Sahan Arzruni, prominent opera sopranos such as Hasmik Papian and more recently Isabel Bayrakdarian and Anna Kasyan. Certain Armenians settled to sing non-Armenian tunes such as the heavy metal band System of a Down (which nonetheless often incorporates traditional Armenian instrumentals and styling into their songs) or pop star Cher. Ruben Hakobyan (Ruben Sasuntsi) is a well recognized Armenian ethnographic and patriotic folk singer who has achieved widespread national recognition due to his devotion to Armenian folk music and exceptional talent. In the Armenian diaspora, Armenian revolutionary songs are popular with the youth.[citation needed] These songs encourage Armenian patriotism and are generally about Armenian history and national heroes.
What famous opera singers used the kef style?