Jack grew up in Santa Monica. He is best known for being an actor. He also sings, he is one half of duo Tenacious D. Jack has appeared in the movies Dead Man Walking (1995), Cradle Will Rock (1999), Demolition Man (1993), The Cable Guy (1996), Jesus' Son (1999), High Fidelity (2000), Shallow Hal (2001), School of Rock (2003), Envy (2004), King Kong (2005), as well as many others.