Conor Cruise O'Brien may or may not be ``the greatest living Irishman'' or ``the most important Irish nonfiction writer of the 20th century,'' but he has certainly found a splendid biographer in historian Akenson (History/Queen's Univ., Ontario). Born in 1917, O'Brien could seemingly do everything but math. He supported himself with prizes at university; wrote literary criticism; was on the fast track in the Irish Foreign Office until he jumped off it, carrying out too exactly the unattributable wishes of UN Secretary-General Dag Hammarskjîld; was vice chancellor of the University of Ghana, a New York academic, an Irish Cabinet minister, editor-in-chief of The Observer, and the author of seminal books on Ireland and Edmund Burke. Along the way he became the enfant terrible of the UN, not only revealing in his To Katanga and Back how it worked but doing it in such entertaining fashion that Akenson calls it ``the first successful picaresque novel of postcolonial Africa, but...a novel that is built almost entirely of fact.'' He showed enormous courage in Ireland, denouncing the constitutionally asserted right of the South to exercise jurisdiction over Ulster as ``essentially a colonial claim'' and campaigning ceaselessly against the romanticization of violence. It would be surprising, in a life devoted to journalism and crusades of one kind or another, if O'Brien had not gone off the rails from time to time as he did in the late 1960s: His castigation of Western imperialism as ``one of the greatest and most dangerous forces in the world today'' and his statement that containing communism was one of the greatest dangers to world peace suggest his limitations. But his courage, his honesty, his restless mind, and his eloquent writing assured him of a wide audience, and his States of Ireland and The Great Melody have both been remarkably influential books, the latter, according to Akenson, ``among the great biographies of the 20th Century.'' This, too, is a very fine biography, full of wit, verve, candor, and a critical appreciation of its subject.