From a Tate Britain online description:

Although Blake was considered mad by contemporaries for his idiosyncratic views, he is held in high regard by later critics for his expressiveness and creativity, and for the philosophical and mystical undercurrents within his work. His paintings and poetry have been characterised as part of the Romantic movement and as “Pre-Romantic”. A committed Christian who was hostile to the Church of England (indeed, to almost all forms of organised religion), Blake was influenced by the ideals and ambitions of the French and American Revolutions.

William Blake (28 November 1757 – 12 August 1827) was an English poet, painter, and printmaker. Largely unrecognised during his lifetime, Blake is now considered a seminal figure in the history of the poetry and visual arts of the Romantic Age. What he called his prophetic works were said by 20th-century critic Northrop Frye to form “what is in proportion to its merits the least read body of poetry in the English language”. His visual artistry led 21st-century critic Jonathan Jones to proclaim him “far and away the greatest artist Britain has ever produced”. In 2002, Blake was placed at number 38 in the BBC’s poll of the 100 Greatest Britons.

To read more: https://www.tate.org.uk/art/artists/william-blake-39