Kirk Windstein is an American musician. He is the frontman, vocalist, rhythm guitarist, and sole constant member of the sludge metal band Crowbar. He is also a founding member of the heavy metal supergroup Down, playing guitar with them from 1991 to 2013 and later rejoining the band in 2020. In 2005, Windstein formed Kingdom of Sorrow with Jamey Jasta of Hatebreed. Their debut album was released in 2008. Windstein began his musical career in 1985 as a guitarist for a cover band called Victorian Blitz, and in 1988 joined a hardcore punk band called Shell Shock as a vocalist and guitarist.

Crowbar is an American sludge metal band formed in New Orleans, Louisiana, in 1990. The band is fronted by vocalist/guitarist Kirk Windstein, Crowbar's sole constant member. Through infusing a slow, low-keyed, brooding doom metal sound with the aggression of hardcore punk, they pioneered a style known as sludge metal – albeit Windstein admitted a mild dislike to the term – alongside other bands of the New Orleans heavy metal scene such as Eyehategod, Soilent Green, Acid Bath, and Down.