Jack the Joker are a progressive metal band from Fortaleza, Ceará, Brazil, formed in 2014 and comprising Raphael Joer on vocals, Felipe Facó and Lucas Colares on guitars, Gustavo Pinheiro on bass, and Vicente Ferreira on drums. A defining characteristic of the band is their integration of traditional northeastern Brazilian rhythms — maracatu, forró, baião, and frevo — into dense progressive metal arrangements. Their discography includes In the Rabbit Hole (2014), Mors Volta, and The Devil to Pay in the Backlands (2025), the latter inspired by João Guimarães Rosa's landmark 1956 Brazilian novel.

Jackhammer are a power/thrash metal band from Jandira, São Paulo, Brazil. Founded by Leo Axekiller (bass/vocals), Marcelo Barbosa (guitar/vocals), and Bruno Barbosa (drums), the band draws from American thrash metal, German metal, NWOBHM, and hardcore influences. They released their debut album Hard to Be Alive in 2009 and have remained active in the São Paulo metropolitan area's metal circuit.

Jatere is a thrash/death metal band formed in Asunción, Paraguay in 2025. They released their debut demo "La muerte no da risa" in December 2025, a three-track release with Spanish-language titles that showcases their aggressive crossover of thrash and death metal influences.

Jaue is a pagan black metal solo project founded in 2020 by Julián David Trujillo Moreno in El Carmen de Viboral, Antioquia, Colombia, and released through Satanath Records. The project draws on Latin American ancestral thought and released its debut full-length, "Cantos del sur salvaje", in 2023.

Jeff Metal is a neoclassical power metal solo project from Brazil, with all instruments and vocals handled by Jefferson Moura Melo. The project blends classical composition with power metal energy and incorporates Christian lyrical themes. The debut album God Created Rock was released in 2020.

Jesters & Klowns are a heavy/power metal band from Córdoba, Argentina, whose current lineup consists of Fer Melian (guitar/backing vocals), DD Garcia (drums), and Lahied (bass). The band released their debut album "The Joker King" on March 27, 2018, a ten-track, 56-minute record blending power metal and hard rock. The album is available on Spotify, Apple Music, and Bandcamp.

Jesushed is a thrash and heavy metal band founded in 2014 by Fabio Curtis in Mogi das Cruzes, São Paulo, Brazil. Drawing on Christian faith without being a strictly gospel act, the band's songs address current events, biblical narratives, and social themes. Their discography spans the debut album Born Again (2014), the EPs 350 graus (2016), Fim dos tempos (2018), and Supermother (2020), with Curtis handling vocals, guitars, and production throughout.

Jezebeth was an atmospheric and melodic black metal band formed in 2021 in Sogamoso, Boyacá, Colombia, active until 2023. The duo — instrumentalist Moctum and vocalist Astaroth Rsse — released the EP "Where Decay Dwells" in 2022 before disbanding, exploring themes of melancholy, sorrow, and love.

Jheronimus Bosch were a progressive/stoner metal band from Pilar, Buenos Aires, founded in 2003 by vocalist and guitarist Lautaro Lunadei and bassist Alejandro Oteiza, with guitarist Ignacio Cruz and drummer Jorge Vega completing the definitive lineup. The band released their self-titled EP in 2008 as well as a subsequent album titled "Ø," both independently. They were active until around 2014 when the band split up.