Marko Tapani "Marco" Hietala (born 14 January 1966) is a Finnish heavy metal vocalist, bass guitarist and songwriter. Internationally, he is most known as the current bass guitarist, 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.