Short answers, pulled from the story.
Henry Fuseli (1741-1825) was a Swiss painter, draughtsman, and writer who spent much of his career in Britain. He is best known for The Nightmare, exhibited in 1782, a painting depicting a sleeping woman with a demon crouching on her chest, and for his influence on artists including William Blake.
The Nightmare, first exhibited in 1782, depicts a sleeping woman pinned beneath a crouching demon. Its themes of horror, dark magic, and sexuality recurred in later works such as Night-Hag visiting the Lapland Witches in 1796. Fuseli painted several versions of The Nightmare.
Fuseli was forced to leave Switzerland in 1761 after helping his friend Johann Kaspar Lavater expose an unjust magistrate, whose powerful family sought revenge against both men. He then travelled through Germany before visiting England in 1765.
Fuseli served as Professor of Painting at the Royal Academy from 1799 and was appointed Keeper in 1803. He resigned the professorship at that point but resumed it in 1810, holding both posts simultaneously until his death in 1825.
Fuseli's Milton Gallery was a series of forty-seven paintings drawn from the works of John Milton, exhibited in 1799 as a counterpart to John Boydell's Shakespeare Gallery. The exhibition was a commercial failure and closed in 1800.
Fuseli's pupils included David Wilkie, Benjamin Haydon, William Etty, and Edwin Landseer. William Blake was also inspired by him. Fuseli himself drew heavily from the study of Michelangelo and classical antiquity, which he pursued during his eight years in Rome from 1770 to 1778.