Mark Zelen is originally from Pittsburgh, Pennsylvania. He started playing guitar at age 15. Frustrated with a lack of available competent bass players with whom to play, Mark took up the instrument himself at age 18, aiming to “become the bass player I couldn't find.” While in college, he played both guitar and bass in a number of rock and jazz situations.

In 1990, Mark played bass in the band Let's Kill Larry. The group opened for a little-known touring act at the time just outside of Philadelphia - that band was called Nirvana. The Pittsburgh music scene was flourishing, and soon thereafter, Mark joined critically-acclaimed local buzz band Bitter Delores. Through extensive touring on the East Coast, Bitter Delores gained much notoriety and a huge fan base. They played in New York, D.C., Boston, Toronto, New Orleans, and a number of other large cities. Among the songs that received airplay in regular rotation (on stations such as WDVE 102.5FM  and WXDX 105.9FM ) was “Floss”, written by Mark.

Along with Nirvana, Mark has shared stages and bills with an impressive roster of acts, including The Violent Femmes, Modern English, Blink 182, Green Day, Culture Club, and Pat Benetar. Bitter Delores eventually disbanded, and in 2000, Mark decided to head to the West Coast. Soon after his arrival, he met up with Drew Conrad and took up bass duties for Willoughby Station. In 2003, Mark and Drew together saw fit to redefine the band and formed ALSO with drummer Scotland Stephenson.