[frankPants]

I'd go with either Mondrian, or Pollock myself. Impressionists, such as Monet began working towards abstraction for sure, but for Monet, it was more about capturing the fleeting nature of light on a canvas, however still within the confines of a landscape.

Surely painting as a pure form of expression, unbridled by anything more than simply paint, reached it's high point with the likes of Mondrian, Pollock, Kandinsky etc during the early 20th century. When composition, colour and form were key and principle elements of the canvas, not nature, and the natural world around. They may have drawn inspiration from the world around but they did not seek to visual represent it on the canvas per se.