Saul Bellow died in 2005. He won the Nobel Prize for Literature in 1976. The first installment of Zachary Leader’s exemplary, scrupulous, dispassionate, detailed, well-read, enthralling biography runs to over 800 pages and takes us only as far as 1964. The length is important. It allows Leader to adjudicate calmly, weigh the evidence — sometimes remaining undecided — and quote Bellow freely, so that the biographical narrative is enlivened by Bellow’s prodigally gifted prose, little injections of bliss.