Poet, critic, impresario, gadfly, visionary, tastemaker: more than anyone, Guillaume Apollinaire embodies the frenzied art world of Paris in the early 20th century. His rampant enthusiasms and antipathies, and his remarkable acumen, make him still today the most evocative commentator on the intellectual ferment of the time. In 1905 he championed Picasso and in 1907 he promoted Braque in reviews that were amazingly sharp and prescient. He first identified...