William L. Howerdel is an American musician, best known as a founding member, guitarist, backing vocalist, songwriter, and producer for the band A Perfect Circle, as well as for his former solo project, Ashes Divide. Howerdel has recorded six studio albums across his career: four with A Perfect Circle, one under the moniker Ashes Divide, and one under his own name.

A Perfect Circle is an American rock band formed in Los Angeles, California in 1999 by guitarist Billy Howerdel and Tool vocalist Maynard James Keenan. A Perfect Circle released three of their four studio albums in the early 2000s: their debut Mer de Noms in 2000, a follow-up, Thirteenth Step in 2003; and an album of radically re-worked cover songs, Emotive, in 2004. Shortly after Emotive's release, the band went on hiatus; Keenan returned to Tool and started up solo work under the band name Puscifer, while Howerdel released a solo album, Keep Telling Myself It's Alright, under the moniker Ashes Divide. Band activity was sporadic in the following years; the band reformed in 2010, and played live shows on and off between 2010 and 2013, but fell into inactivity after the release of their greatest hits album, Three Sixty, and a live album box set, A Perfect Circle Live: Featuring Stone and Echo in late 2013. The band reformed in 2017 to record a fourth album, Eat the Elephant, which was released in 2018. After spending the rest of the year touring in support of the album, the band fell into inactivity until 2024 for a brief tour and one-off song "Kindred".