Sometimes musicians play for other bands or create their own for a variety of purposes - to explore new sounds, to play with other people, or to escape the clutches of their industrial overlords. Whatever the case may be, they are called side projects mainly because that's what they are supposed to be - a side project - instead of their main projects.

There are cases when these supposed experiments or passion projects turn into something big. Here are five big acts that started out at someone else's side project.

1. Fall Out Boy

Pete Wentz was already a "visible fixture" of Chicago's local hardcore punk scene, performing in bands Birthright, Extinction, First Born. Wentz played on Racetraitor with Andy Hurley as the drummer. Wentz also played with FOB lead guitarist Joe Trohman on the metalcore act Arma Angelus. Patrick Stump played drums for local hardcore punk bands.

fall out boy
(Photo : Fall Out Boy's YouTube Channel)

What became Fall Out Boy actually started as an easy and escapist project for Wentz and Trohman, playing pop-punk instead of their forte hardcore punk. They later got Stump and Hurley to join, although Hurley was both busy and uninterested. Despite limited opportunities and having Wentz and Stump argue from the band's name to the songwriting, Fall Out Boy was born and the rest is history.

READ MORE: Fall Out Boy: The Phoenix From Under The Cork Tree

2. Gorillaz

Damon Albarn was already gaining fame as the frontman for the British alt-rock band Blur. In 1990. Guitarist and co-founder Graham Coxon asked Jamie Hewlett to interview their band, which was published in "Deadline" magazine where Hewlett released his comic strip "Tank Girl." 

(Photo : Parlophone Records' YouTube Channel)

READ MORE: Virtual Band Gorillaz To Release Their Own Almanac Later This Year

Although they didn't get along at first, the two somehow became flatmates in 1997. They got the idea for the side project "Gorillaz" after watching MTV and decided to create a "virtual band" as a commentary. Albarn and Hewlett created Gorilla and recorded "Ghost Train." The iconic lineup of Noodle, Stuart "2D" Pot, Russel Hobbs, and Murdoc Niccals appeared on the music video for "Clint Eastwood," released in 2001.

3. The Travelling Wilburys

It was basically a supergroup on its own right, with members such as Bob Dylan, The Beatles' George Harrison, Electric Light Orchestra's Jeff Lynne, The Heartbreakers' Tom Petty, and Roy Orbison. 

This British-American side project started from Harrison and Lynne's discussion during the recording of his 1987 studio album "Cloud Nine." The group released two studio albums "Traveling Wilburys Vol. 1" and "Traveling Wilburys Vol 3."

4. Bon Iver

What the world now know as one of the largest indie acts actually started as a side project for its frontman Justin Vernon. He was already a musician in 1997, forming his first band Mount Vernon. He then founded DeYarmond Edison while he was attending college in 2001, with Megafaun member Phil Cook and Field Report frontman Christopher Porterfield.

During his tenure with Volcano Choir, Vernon created Bon Iver, which was actually a solo project before growing into a full band. He started earning international fame with Bon Iver's debut album "For Emma, Forever Ago."

5. Pinhead Gunpowder

This punk rock mainstay has lasted for two decades, and its lineup included music editor Aaron Cometbus, punk rock bassist and songwriter Bill Schneider, Green Day frontman Billie Joe Armstrong and their touring guitarist Jason White.

While it has been a decade since their last performance on Berkley, California, Pinhead Gunpowder has risen to the top of the US punk rock scene with hits like "Big Yellow Taxi" (1994), "Buffalo" (2001), and "Beastly Bit" (2001).