Jón Þór "Jónsi" Birgisson (pronounced [ˈjouːn ˈθouːr ˈpɪrcɪsɔːn, ˈjounsɪ] (listen); born 23 April 1975) is an Icelandic musician; he is the vocalist and multi-instrumentalist for the Icelandic post-rock band Sigur Rós. He is known for his use of a cello bow on guitar and his "angelic" falsetto or countertenor voice. He is blind in his right eye from birth as a result of a broken optic nerve from the brain. He is openly gay. Apart from Sigur Rós, Jónsi also performs together with his ex-partner Alex Somers as an art collaboration called Jónsi & Alex. They released their self-titled first book in November 2006, which was an embossed hardcover limited to 1,000 copies. The two also released the album Riceboy Sleeps, in July 2009. They announced their separation in 2019, after having been together for 16 years.On 1 December 2009, Jónsi's official website, jonsi.com, was launched in anticipation of his debut solo album, Go, which was released on 5 April 2010. After the release of the album, Jónsi promptly started a tour across North America and Europe, featuring songs from the album plus a few other selections, planning to tour from March to September. A decade would pass before Jónsi would release his second studio album, Shiver, which was released on October 2, 2020. He would release his third album Obsidian a year later in conjunction with the exhibit of the same name.

In late January 2010, Jónsi announced that Sigur Rós was on "an indefinite hiatus", as the band had scrapped plans for a new album previously announced to be released in 2010, saying that "they were just rumours". The band decided to take the year off, as several members of Sigur Rós recently had children, and as Jónsi developed his solo career. In 2012, the band reformed and released the album Valtari in May 2012 and subsequently Kveikur in June 2013.