Kevin Oluwole Olusola, also known as K.O., is an American singer-songwriter, beatboxer, and cellist. Olusola is best known as the beatboxer of the a cappella group Pentatonix. After the group won NBC's The Sing-Off in 2011, they released eleven albums, which have sold over 2 million records, and have amassed more than two billion views on their YouTube channel.