United States of America is a country which is basically ruled by a president. Each president has a chance to lead the country for 4 years, and he also has the chance to postulate in the next 4 year elections. The limit for any president is 8 years regardless of how well he ruled.
So far there has not been a Woman elected for presidency. The first woman who postulated herself to the elections in 2008 was Hillary Clinton, wife of ex-president Bill Clinton.
Currently the country's president's name is Barack Obama which incidentally is the first Afro-American president, in the history of the United Stated of America.