The facts of Theodor Geisel's life are not as well known as his illustrious works, but in this authorized biography (from Geisel's own publisher), they're nearly as exuberant. Despite the title's play on Jekyll and Hyde (Geisel loved Stevenson), the authors present a man no less entertaining and eccentric in private and in person than in public and in print. Judith (coauthor of California, not reviewed) and Neil (Westward Tilt, not reviewed) Morgan had access to their subject's unfinished autobiography and other papers, and they draw on interviews with Geisel and his collaborators to paint a clear picture of Geisel's high-spirited childhood in Illinois; his unsuccessful pursuit of a Ph.D. in English literature at Oxford; his early break in cartoons and advertising with his "Quick, Henry, the Flit!" insecticide series; and his successful switch to children's books in 1937 with And to Think That I Saw It on Mulberry Street. There are likewise modest revelations about his career (his pseudonym first appeared when the president of Dartmouth banned him from the campus humor magazine because of a bootleg gin party) and his creative personality (whimsy and ebullience mixed with perfectionism and shyness). Geisel's career took off meteorically with the convergence of demographics and technology; rebelling against Dick and Jane dullness, baby boomers exultantly devoured his fantastic yet simply written, colorfully lithographed tales. Even as a national treasure and publishing institution, he remained unpredictable, creating such bestsellers as You're Only Old Once! for grown-ups. The Morgans tell the success story well, but they neglect darker spots such as Geisel's sudden second marriage after his first wife's suicide and his his opportunistic desertion of his first publisher for the burgeoning Random House. Competent, if uninsightful, in discussing Geisel's place in American culture, the Morgans tend to heap adulation on the creator of Ooblek, the Lorax, and Sneetches.