Over my many years writing editorials about New York for The New York Times, the city’s political class had a preferred list of adjectives for then mayor Michael Bloomberg: staid, stoic, irritable, irritating, distant, insensitive, gray—or any synonym for boring. Bloomberg can indeed earn all of those descriptions, I found, as I produced an unauthorized biography of this powerful billionaire. But underneath the cardboard, he is a complicated man who can be funny, smart, raunchy, generous, gutsy (an early foe of the N.R.A.), persuasive, and hell-bent on being the kind of better billionaire that Donald Trump isn’t.

At heart, Bloomberg is also a salesman who wants you to buy into his view of the world (or, failing that, what about one of his Bloomberg data terminals at $24,000 a year?). A trained engineer, he wants to fix things, even a gun-plagued America and a warming planet. He’s announced plans to spend $500 million fighting climate change and even more on the elections next year. At about one percent of his net worth, that is almost certainly a down payment.