Pingyang County’s verdant hills still hint at a long-lost China. Rice paddies and villages surround its bustling towns, and in the fields, farmers wade into the mud to plant seedlings as they have for thousands of years. It is an odd place to find the people behind a Chinese corporate powerhouse that is turning heads on Wall Street with a global takeover binge. Yet the area is home to a tiny group of just such people — small-time merchants and villagers who happen to control multibillion-dollar stakes in the Anbang Insurance Group, which owns the Waldorf Astoria in New York and a portfolio of global names and properties. American regulators are now asking who these shareholders are — and whether they are holding their stakes on behalf of others. The questions add to the mystery surrounding a company that seemed to come out of nowhere, surprising deal makers with offers to pay more than $30 billion for assets around the world.