6. Ellen Johnson Sirleaf, President of Liberia

Ellen Johnson Sirleaf, the first elected female head of state in Africa, has been president of Liberia since 2006.

The 73-year-old Harvard graduate has been nicknamed Liberia's Iron Lady for her political resilience and tough reputation. She, together with Leymah Gbowee of Liberia and Tawakel Karman of Yemen, was awarded the 2011 Nobel Peace Prize, in recognition of her efforts to further women's rights.

In 2010, Newsweek listed her as one of the ten best leaders in the world and Time magazine counted her among the top ten global female leaders. That same year, The Economist called her "arguably the best president the country has ever had."

7. Park Geun-hye, President of South Korea

Park Geun-hye, nicknamed the Queen of Elections, has followed in the footsteps of her late father, former South Korean President Park Chung-hee, by winning the presidency in December 2012.

She will become the first female president of Asia's fourth-largest economy after taking office in February 2013.

8. Portia Simpson-Miller, Prime Minister of Jamaica

Portia Simpson-Miller defeated Prime Minister P. J. Patterson in the 2006 general election, becoming the first female head of the Jamaican government. She was elected prime minister of the nation for a second term in December of 2011, assuming office in January 2012.

Simpson-Miller was ranked among Time's 100 Most Influential People in the World in 2012, and named Person of the Year by The Gleaner and Observer at the 2011 Gleaner awards.

9. Johanna Sigurdardottir, Prime Minister of Iceland

Johanna Sigurdardottir became Iceland's first female prime minister and the world's first openly homosexual head of government in February 2009.

In 2009, Forbes listed her among the 100 Most Powerful Women in the world. In September 2012, Jóhanna announced she would not seek re-election and would instead retire from politics.

10. Helle Thorning-Schmidt, Prime Minister of Denmark

Helle Thorning-Schmidt was elected as the first female prime minister of Denmark in 2011, breaking the grip of center-right parties on this Scandinavian nation and bringing the social democrats back into the government after a decade of opposition.

Her election signified a coalition between the three center-left parties, namely the Social Democratic Party, of which she is chairman, the Social Liberal Party and the Socialist People's Party. These three form the minority government that will run this small Nordic country of 5.5 million people over the next four years.