Book excerpt: Despite limited legal power, the job of the United Nations secretary-general has evolved into that of an often-effective global leader and mediator. When the Security Council is blocked - and sometimes even when it isn't - the UN's top official has played a key role in resolving international disputes. This book looks at the varied ways that the eight secretaries-general -- from risk-takers to cautious conservatives - have used their position to pursue the common goal of a more peaceful world.