Karl Matthew Alvarez (born March 10, 1964) is an American bassist and songwriter for both the Descendents and All, the band that resulted after the Descendents disbanded again in 1987. Alvarez joined the Descendents after the Enjoy! album from his previous band The Massacre Guys, and played on all of the All albums, and the Descendents albums All, Everything Sucks and Cool To Be You. He plays finger style bass and provides backing vocals when live (and lead vocals as heard in "Cause" on the All Live Plus One album). Since joining the band he has been a major songwriter contributing many songs to All (both the album and the band), Everything Sucks and Cool To Be You. In the summer of 2006 he joined Gypsy Punk band Gogol Bordello for part of the Van's Warped Tour and the Reading and Leeds Festivals. Karl currently plays guitar and sings in Underminer and the Vultures.