The Spanish Cubist painter referred to in the crossword solutions is Pablo Picasso, whose surname has 7 letters, and Juan Gris, whose surname has 4 letters. Picasso was a renowned artist who co-founded the Cubist movement and is widely considered one of the most influential artists of the 20th century. Gris was a Spanish painter who was heavily influenced by Picasso's work and was an important figure in the development of Cubism.