Mary, Queen of Scots

1542-1587.
She was an heir to the Scottish king James V and inherited the throne on December 14, 1542, when she was only six days old.
In 1548 she was sent to France to live at the court of Henry II of France and was betrothed to the Dauphin, Francis, whom she married in 1558. When Henry II died, Mary and Francis reigned over France and Scotland but Mary also claimed the throne of England and Ireland.
Francis died on December 5, 1560, the couple was childless. Due to a contract made with Henry before her marriage, Mary could stay in France or go back to Scotland. She decided to go back to her home country Scotland in August, 1561.
She married again, Henry Stewart, Lord Darnley who was a Catholic but later allied with the Protestants. Mary and Henry are the parents of James VI of Scotland, who later became James I of England. On February 10, 1567 Darnley was murdered and only a few months later Mary married James Hepburn, Earl of Bothwell, rumoured to be one of the murderers of her ex-husband. That is one of the reasons why Mary was accused to be a member of the murderers of Darnley and forced to abdicate. The tension between Mary’s supporters and enemies rose and on May 2, 1568 after Mary had been captured for about one year at Lochleven Castle; she could escape and joined forces with the Hamilton family in the West. She decided to appeal to Elizabeth I, her cousin, Queen of England, and to flee to England as well. She would never see Scotland again.
Since Elizabeth was childless and could imagine that Mary’s son James could become her heir as well, she considered Mary, being the closest Catholic claimant to the English throne, as some kind of danger to her own power. Elizabeth kept Mary as a prisoner although at this time the claim that Mary was one of the murderers of Darnley met some counter evidences.
There could also be some evidence in the so-called Casket Letters, letters written between Mary and Bothwell but it is unclear whether they really existed and if yes, what was written in them because the originals are not existant and only some translated copies exist today.
In any case, Mary was accused of conspiring against Elizabeth and found guilty after the abortive Babington Plot. She was last kept at Fotheringhay Castle, where she was also executed in 1587. There are also some juicy facts known about her execution: the executioner was not able to cut her head off at the first blow, so he had to try it with a second one. When he wanted to show the head to the audience he was only carrying Mary’s wig, her head still lying on the ground.

Sources:
Cannon, John Ashton. The Oxford Companion to British History. Oxford, 1997.
MacKay, James. In My End is My Beginning - A Life of Mary Queen of Scots. Edinburgh, 2000.
http://www.bbc.co.uk/history/historic_figures/scots_mary_queen_of.shtml
Wormald, Jenny. Mary, Queen of Scots. Politics, Passion and a Kingdom Lost. London and New York, 2001.