David Warren Ellefson (born November 12, 1964) is an American musician. He was the bassist and co-founder of the heavy metal band Megadeth from 1983 to their breakup in 2002, and again from 2010 to 2021. In addition to playing bass guitar in Megadeth, Ellefson has various side projects, which include Temple of Brutality, F5, Killing Machine, and Metal Allegiance.