Justin Gunnar Walter Chancellor is an English musician, best known as the bassist for rock band Tool, a position he has held since 1995. Prior to joining Tool, he played in a band called Peach. After settling in the US, along with his engagement in his musical projects, he and his wife Shelee Dykman Chancellor ran a store called Lobal Orning in Topanga, California, dedicated to music and literature "that shaped and changed" both of them. The store closed in 2008. He started M.T.Void music project with Piotr "Glaca" Mohammed from Sweet Noise.

Tool is an American rock band from Los Angeles. Formed in 1990, the group consists of vocalist Maynard James Keenan, guitarist Adam Jones, drummer Danny Carey and bassist Justin Chancellor, the latter of whom replaced founding member Paul D'Amour in 1995. Tool has won four Grammy Awards, performed worldwide tours, and produced albums topping the charts in several countries.