When her husband, Bill Clinton, ran for President in 1992, he told voters that they would be getting "two for the price of one." As First Lady, Hillary Clinton spoke out on several causes. In 2000, she was elected to the U.S. Senate for New York. Her attempt to become the first woman President of the U.S. failed in 2008. She served as Secretary of State from 2009 until 2013. Some political experts predict she will run for President again in 2016. (1947—present)

On December 1, 1955, in Montgomery, Alabama, Rosa Parks would not give up her seat on a bus to a white passenger. Her simple act landed Parks in jail. But it also set in motion the Montgomery bus boycott. It lasted for more than a year, and kicked off the civil-rights movement. "The only tired I was, was tired of giving in," said Parks. Her historic act demonstrated the power of peaceful protest. (1913—2005)

Anyone who has ever been helped by a social worker has Jane Addams to thank. Addams helped the poor and worked for peace. She encouraged a sense of community by creating shelters, education opportunities and services for people in need. In 1931, Addams became the first American woman to win the Nobel Peace Prize. (1860—1935)

When Sandra Day O'Connor finished third in her class at Stanford Law School, in 1952, she could not find work at a law firm because she was a woman. She became an Arizona state senator and, in 1981, the first woman to join the U.S. Supreme Court. O'Connor cast the deciding vote in many important cases during her 24 years on the top court. (1930—present)

In 1979, Margaret Thatcher became Britain's first female Prime Minister. She served until 1990, which makes her the only British leader to serve three consecutive terms. Her high standards and strong will earned her the nickname Britain's Iron Lady. (1925—present)

Polish-born scientist Marie Curie discovered that some elements give off energy called radiation. Her research led to new medical treatments and weapons. She received the Nobel Prize in Physics in 1903 and in Chemistry in 1911. She paved the way for women scientists. (1867—1934 )

If it weren't for Rachel Carson, the environmental movement might not exist today. Her popular 1962 book Silent Spring raised awareness of the dangers of pollution and the harmful effects of chemical pesticides on humans and on the world's lakes and oceans. (1907—1964 )

In 2005, Germans chose Angela Merkel as their first female Chancellor, or head of government, because they knew that they could rely on her steady hand. Merkel was a physicist before going on to a second career in politics. As Germany's leader, she has become a worldwide political force. (1954—present)

Having grown up poor, Oprah Winfrey overcame many obstacles to become an entertainment star, an author, a businesswoman and a philanthropist. Her national TV show first aired in 1986. Now, Winfrey helps people in many ways, oversees a magazine and runs a television network. (1954—present)

As a Roman Catholic nun, Mother Teresa devoted her life to helping the very poor. She received the Nobel Peace Prize in 1979 for her charity work caring for the poor, the hungry and the sick in India. (1910—1997)