And here is one of the best biographical sketches I've read about Beckmann, by Dr. Harold Joachim.
Here's a good part:
His art, too, may at first appear blunt and aggressive, but those who study it will soon discover not only a profound visionary mind, but one of the most sensitive hands in modern art, a hand not only of a master draftsman who had been able to compress the diversity of the visible world into a hieroglyphic language of his own, but also of a master painter who was highly sensitive to surface texture and color relationships. It is no wonder that these qualities, so rare among German Expressionists, gained him the respect, if not the love, of the French.
Although he is now universally considered one of the major figures of German Expressionism, Beckmann himself disdained any such classification...