Tuomas Lauri Johannes Holopainen is a Finnish musician, songwriter, and record producer, best known as the primary songwriter, keyboardist, and a co-founding member of symphonic metal band Nightwish. He has stated that his songwriting is influenced by harmonic film music.

Nightwish is a Finnish symphonic metal band from Kitee. The band was formed in 1996 by lead songwriter and keyboardist Tuomas Holopainen, guitarist Emppu Vuorinen, and former lead singer Tarja Turunen. The band soon picked up drummer Jukka Nevalainen, and then bassist Sami Vänskä after the release of their debut album, Angels Fall First (1997). In 2001, Vänskä was replaced by Marko Hietala, who also took over the male vocalist role previously filled by Holopainen or guest singers. Although Nightwish have been prominent in their home country since Angels Fall First, they did not achieve wider success until the release of the albums Oceanborn (1998), Wishmaster (2000) and Century Child (2002).