One part biography, one part prayer book, The Life and Prayers of Mother Teresa is an essential for any Christian. Mother Teresa wanted to do "something beautiful for God." At the time of her death in 1997, there were nearly 4,000 Missionaries of Charity Sisters established in 610 houses in 123 countries. The congregation did not cease growing with her death. Today, there are more than 5,000 Sisters. The work continues to thrive as the network of Missionaries of Charity continues to operate centers in countries throughout the world. In 1985, Mother Teresa was invited to address the United Nations General Assembly. On that occasion, the Secretary General of the United Nations, Javier Pérez de Cuéllar, called her "the most powerful woman in the world." At the end of 1999, two years after Mother Teresa's death, Gallup published a poll of America's most widely admired people of the 20th century. Mother Teresa topped the list, ahead of such luminaries as Rev. Martin Luther King, Jr., Helen Keller, Winston Churchill, and Albert Einstein.