(see The Great Red Dragon paintings)
The Wikipedia article is a good place to begin, but I want to concentrate on Blake as an exemplar of dream vision and imagery, and as a cross-link to Swedenborg and the familial multi-generational entanglement in my own life.
Blake's parents were participants in the Moravian Brotherhood which Swedenborg frequented during his London years in the 1740s, a fascinating milieu to explore further but a digression here (see A Time of Sifting (Paul Peucker) and a fascinating review of that book; and The Erotic Dreams of Emanuel Swedenborg [Richard Lines] to pique further curiosity...).
But our interest here and now is with Young William Blake and the Moravian Tradition of Visionary Art (Schuchard), and with Blake's dreamlike images, which began with his meetings with angels on Peckham Rye, his apprenticeship to an engraver, and his experiments with painting, often expressive of dream imagery. A few examples, to whet the whistle for a deeper dive into Blake's originality and peculiarity: