Wikipedia article

Matt Sweeney was the first additional member of Zwan, formed by then-former Pumpkins Billy and Jimmy in 2001. Previously, Matt had performed in bands Chavez and Skunk, who were mentioned and praised by Billy in the liner notes of Pisces Iscariot while discussing Frail and Bedazzled. Matt then recruited David Pajo, who joined Zwan on bass, but switched to guitar the following year after bassist Paz Lenchantin joined.

In addition to guitar duties, Matt sang the Iron Maiden cover "Number of the Beast", which appears on the Honestly single and was featured in the movie Spun. After Zwan split in 2003, Matt collaborated and released more material with Bonnie "Prince" Billy and several other artists, and has done production work for Dax Riggs, Early Man, and Probot, a metal side project band by Dave Grohl featuring different metal vocalists on each track.