Zurvanism is a now-extinct branch of Zoroastrianism in which the divinity Zurvan is a First Principle (primordial creator deity) who engendered equal-but-opposite twins, Ahura Mazda and Angra Mainyu. Zurvanism is also known as "Zurvanite Zoroastrianism", and may be contrasted with Mazdaism, which is the surviving form of Zoroastrianism and in which Ahura Mazda and Angra Mainyu are either themselves primordial (the traditional view), or the 19th/20th century developments in which Ahura Mazda is no longer the Creator of only the good, but also perceived as the origin of Angra Mainyu.