Gruen has worked with acts such as Led Zeppelin, The Who, David Bowie, Tina Turner, Elton John, Aerosmith, & KISS. He toured with emerging punk and new wave bands including the Sex Pistols, the Clash, the Ramones and Blondie, and currently works with Green Day.

In the spring of 2007 FAAP University in Brazil presented an exhibition of Gruenʼ s work titled Rocker, which attracted 40,000 visitors. In November 2010 he was inducted into the Long Island Music Hall of Fame.