Pieter Cornelis "Piet" Mondriaan, after 1912 Mondrian, was a Dutch painter. He was an important contributor to the De Stijl art movement and group, which was founded by Theo van Doesburg. He evolved a non-representational form which he termed Neo-Plasticism. This consisted of white ground, upon which was painted a grid of vertical and horizontal black lines and the three primary colors.