Marko Tapani "Marco" Hietala (born 14 January 1966) is a Finnish heavy metal vocalist, bassist and songwriter. Internationally, he is most known as the current bassist, male vocalist and secondary composer to Tuomas Holopainen, of the symphonic metal band Nightwish. He is also the vocalist and bassist as well as composer and lyricist for the heavy metal band Tarot.
He is also a member of the supergroup Northern Kings, and portrayed one of the main characters in Ayreon's 2013 album The Theory of Everything.
Marco Hietala was born in Tervo, and is the youngest child of the Hietala family. Hietala lived in Tervo until the age of 15, after which he moved to Kuopio to study classical guitar, vocals and musical theory in high school. In 1984, he and his brother, Zachary Hietala, formed heavy metal band Tarot under the name Purgatory. In 1986, Tarot received a deal for their first album and went on tour. Before becoming a full-time musician, he worked as a live and studio sound engineer.