[1] His early works were conventional portraits, landscapes, still lifes, city scenes and historical paintings.
From about 1892 he won a reputation as an "industry artist",[2] painting manufacturing scenes in oils and watercolors.
Kley attained greater notoriety with his sometimes darkly humorous pen drawings, published in Jugend and the notorious Simplicissimus.
A collection of Kley's two published sketchbooks was sold under the title Sammelalbum alter und neuer Zeichnungen (Album of Old and New Drawings) which was banned under the Nazi regime.
[5] Cartoonist Joe Grant was well aware of Kley's work and introduced his drawings to Walt Disney, who built an extensive private collection.