Which central banker has the toughest job in 2006? Incoming U.S. Federal Reserve Chairman Ben Bernanke will need to be vigilant about inflation while getting the timing of interest-rate tightening just right. European Central Bank head Jean-Claude Trichet is likely to push through the first ECB rate hike in five years amid signs that inflation is rising and euro zone economies are finally rebounding. Yet all of that is playground stuff compared to what Zhou Xiaochuan, the governor of the People’s Bank of China, faces. He is under enormous international pressure to orchestrate a steady appreciation of the yuan vs. the dollar while at the same time preventing a spike in inflation in an economy so white-hot it could hit 10% growth in 2006. As a key overseer of China’s bloated banking system, he must also continue reforms to keep bad loans from ballooning.