Sandy Weill’s new book accomplishes what nobody expected it could in the era of the bloated and arrogant business autobiography. “The Real Deal: My Life in Business and Philanthropy” is a refreshingly honest and candid reflection by the most important man on Wall Street in the second half of the 20th century.

Mr. Weill got his start on the Street as a runner at a brokerage house, an experience which influenced how he looked at the financial world during the rest of his meteoric rise through it. What he learned was that as long as he kept a strong forcus on institutional securities, the other parts of the vast financial services companies he built would always fall into place around that core.

Indeed, Mr. Weill tells us that from the founding of Carter, Berlind, Patoma & Weill in 1960, it was his love of interacting with clients and writing transaction tickets that drove him to grow the company that would become, in 1979, Shearson Loeb Rhoades. In 1981, he sold his firm to American Express for $1 billion.

Lesser men would have retired into a life of wealth and obscurity. Mr. Weill, as if he were planning the chapters of “The Real Deal,” instead mounted a Wall Street comeback after leaving American Express in disgust. He took Commercial Credit public and triumphantly bought back Shearson from his old firm.

The merger and acquisition stories that culminate with the Travelers-Citicorp deal reveal just how many presentday titans were once faithful lieutenants to Mr. Weill. We get a hint of what these protégés learned from him. If you stepped in Mr. Weill’s way, for instance, the former brokerage house runner would inevitably run over you. Mr. Weill provides tantalizing accounts of his fall-out with Arthur Carter: “Sadly, our firm’s success fed Arthur’s already outsized ego, and tensions gradually mounted as Arthur increasingly bullied the rest of us.” Arthur Carter was out.

Then there was Citicorp’s John Reed: “I always had put a premium on developing an intuitive feel for my company and acting decisively. John, on the other hand, needed to study everything to death and insisted that managers prepare large briefing ‘decks’ that would examine issues from every angle.”

Mr. Weill, the stockbroker at heart, has never had much use for stiffs in their corporate suites far removed from their firms’ day-to-day operations. It becomes clear in “The Real Deal” that Mr. Weill’s ability to cut to the chase and analyze deals with clarity allowed him to predict — and make way for — the post-Glass Steagall world in which we live today.