A century ago, J. Pierpont Morgan bestrode the financial world like a colossus. The organizing force behind General Electric, U.S. Steel, and vast railroad empires, he served for decades as America's unofficial central banker: a few months after he died in 1913, the Federal Reserve replaced the private system he had devised. An early supporter of Thomas Edison and Andrew Carnegie, the confidant (and rival) of Theodore Roosevelt, England's Edward VII,...