Chuck Billy (born June 23, 1962) is an American vocalist, who is best known as the vocalist for the thrash metal band Testament.Chuck Billy replaced Steve "Zetro" Souza, future Exodus vocalist, in the mid-1980s when the band was still called Legacy. Following his arrival, Testament released their first album entitled The Legacy in 1987. The only song written by Chuck Billy on The Legacy was "Do or Die". Although the lineup of the band has changed over the years, Billy has remained constant as the vocalist alongside guitarist Eric Peterson who also was an all time permanent member. However, his vocal style has changed considerably over the years from a clear, high pitch thrash style to a deeper low register approaching a death grunt. Since the Low album, he has mixed both styles and sometimes performs both on the same song