David Warren Ellefson (born November 12, 1964) is an American bassist, co-founder and second-longest serving member of the American heavy metal band Megadeth from 1983 to 2002 and again since 2010. He has also been referred to as "Junior" to differentiate him from his bandmate Dave Mustaine, but does not go by this name professionally. Ellefson currently resides in Scottsdale, Arizona. In addition to playing bass guitar in Megadeth, Ellefson also has various side projects which include Temple of Brutality, F5, Killing Machine, Metal Allegiance and Altitudes and Attitude.