did he belong to any other band before joining the former one?
Yes, TexA.N.S.
Maynard James Keenan
During the 1980s, Keenan played bass guitar for TexA.N.S. and sang for Children of the Anachronistic Dynasty, both independent bands. During this time, he wrote an early version of "Sober", later Tool's first successful single. 
what is tool? American rock band when did this band form? 1990 who are the members of this band? Danny Carey, Adam Jones and Maynard James Keenan what kind of music is associated with this band? Rock who is the lead singer of this band? Maynard James Keenan where is he from? Ravenna, Ohio
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Maynard James Keenan [SEP] Early bands
Upon completing his term of prep school, Keenan studied art at Kendall College of Art and Design in Grand Rapids, Michigan. From there he moved to Somerville, Massachusetts, where his love of animals led him to practice interior design for a Boston-area pet store. He was transferred to a store in Los Angeles, before he was quickly fired and began working in set construction. During the 1980s, Keenan played bass guitar for TexA.N.S. and sang for Children of the Anachronistic Dynasty, both independent bands. During this time, he wrote an early version of "Sober", later Tool's first successful single. He also (with future Tool bandmate Danny Carey) performed live and recorded with Green Jellö between 1990 and 1993, playing guitar and performing backup vocals as the voice of one of the pigs on the band's hit song "Three Little Pigs" on their debut album "Cereal Killer", and appearing in the music video for "Slave Boy" on the band's follow-up LP "333".