Ren Hang, who took his life February 23, 2017, was an unlikely rebel. Slight of build, shy by nature, prone to fits of depression, the 29-year-old Beijing photographer was nonetheless at the forefront Chinese artists' battle for creative freedom. Like his champion Ai Weiwei, Ren was controversial in his homeland and wildly popular in the rest of the world. He said, "I don't really view my work as taboo, because...