The Book of Urizen is one of the major prophetic books of the English poet William Blake, illustrated by Blake's own plates. It was originally published as The First Book of Urizen in 1794. Later editions dropped the word "first". The book takes its name from the character Urizen in Blake's mythology, who represents alienated reason as the source of oppression. The book describes Urizen as the "primeaval priest", and describes how he became separated from the other Eternals to create his own alienated and enslaving realm of religious dogma.

Los and Enitharmon create a space within Urizen's fallen universe to give birth to their son Orc, the spirit of revolution and freedom. Urizen's first four sons are Thiriel, Utha, Grodna and Fuzon (respectively elemental Air, Water, Earth, Fire, according to Chapter VIII). The last of these plays a major role in The Book of Ahania, published the following year. (Summary from Wikipedia)