William Patrick Niederst (born September 5, 1970), better known as Liam Lynch, is an American filmmaker, singer, musician, songwriter, and puppeteer.

While studying at LIPA in Liverpool, United Kingdom, Lynch co-created, co-wrote, directed, scored, and produced the 1998 MTV comedy puppet series The Sifl and Olly Show. His 2003 album Fake Songs featured the song "United States of Whatever", which peaked within the top ten of the charts in Australia and the United Kingdom. He has since become more known for directing music videos for acts such as Queens of the Stone Age, Foo Fighters, Royal Blood, Tenacious D, Spinnerette, No Doubt, Eagles of Death Metal, "Weird Al" Yankovic, and They Might Be Giants.

Lynch directed the 2006 film Tenacious D in The Pick of Destiny after working with Tenacious D in 2002, having directed the music video for their song "Tribute". He also directed several short films that played as part of their live show, as well as the documentary On The Road with Tenacious D. He also wrote the original music used in the 2002 MTV animated series Clone High and co-wrote a song in the 2003 film School of Rock, as well as directing Sarah Silverman's 2005 stand-up comedy film Sarah Silverman: Jesus Is Magic.