John William Casilear was an American landscape artist belonging to the Hudson River School.
Casilear was born in New York City. His first professional training was under prominent New York engraver Peter Maverick in the 1820s, then with Asher Durand, himself an engraver at the time. Casilear and Durand became friends, and both worked as engravers in New York through the 1830s.
By the middle 1830s Durand had become interested in landscape painting through his friendship with Thomas Cole. Durand, in turn, drew Casilear's attention to painting. By 1840, Casilear's interest in art was sufficiently strong to accompany Durand, John Frederick Kensett, and artist Thomas Prichard Rossiter on a European trip during which they sketched scenes, visited art museums, and fostered their interest in painting.
Casilear gradually developed his talent in landscape art, painting in the style that was later to become known as the Hudson River School. By the middle 1850s he had entirely ceased his engraving career in favor of painting full-time.