<P> Mary, a Roman Catholic, reigned during a period of great religious upheaval in Scotland . As a result of the efforts of reformers such as John Knox, a Protestant ascendancy was established . Mary caused alarm by marrying her Catholic cousin, Lord Darnley, in 1565 . After Lord Darnley's assassination in 1567, Mary contracted an even more unpopular marriage with the Earl of Bothwell, who was widely suspected of Darnley's murder . The nobility rebelled against the Queen, forcing her to abdicate . She fled to England, and the Crown went to her infant son James VI, who was brought up as a Protestant . Mary was imprisoned and later executed by the English queen Elizabeth I . </P> <P> Elizabeth I's death in 1603 ended Tudor rule in England . Since she had no children, she was succeeded by the Scottish monarch James VI, who was the great - grandson of Henry VIII's older sister and hence Elizabeth's first cousin twice removed . James VI ruled in England as James I after what was known as the "Union of the Crowns". Although England and Scotland were in personal union under one monarch--James I became the first monarch to style himself "King of Great Britain" in 1604--they remained two separate kingdoms . James I's successor, Charles I, experienced frequent conflicts with the English Parliament related to the issue of royal and parliamentary powers, especially the power to impose taxes . He provoked opposition by ruling without Parliament from 1629 to 1640, unilaterally levying taxes and adopting controversial religious policies (many of which were offensive to the Scottish Presbyterians and the English Puritans). His attempt to enforce Anglicanism led to organised rebellion in Scotland (the "Bishops' Wars") and ignited the Wars of the Three Kingdoms . In 1642, the conflict between the King and English Parliament reached its climax and the English Civil War began . </P> <P> The Civil War culminated in the execution of the king in 1649, the overthrow of the English monarchy, and the establishment of the Commonwealth of England . Charles I's son, Charles II, was proclaimed King of Great Britain in Scotland, but he was forced to flee abroad after he invaded England and was defeated at the Battle of Worcester . In 1653, Oliver Cromwell, the most prominent military and political leader in the nation, seized power and declared himself Lord Protector (effectively becoming a military dictator, but refusing the title of king). Cromwell ruled until his death in 1658, when he was succeeded by his son Richard . The new Lord Protector had little interest in governing; he soon resigned . The lack of clear leadership led to civil and military unrest, and for a popular desire to restore the monarchy . In 1660, the monarchy was restored and Charles II returned to Britain . </P> <P> Charles II's reign was marked by the development of the first modern political parties in England . Charles had no legitimate children, and was due to be succeeded by his Roman Catholic brother, James, Duke of York . A parliamentary effort to exclude James from the line of succession arose; the "Petitioners", who supported exclusion, became the Whig Party, whereas the "Abhorrers", who opposed exclusion, became the Tory Party . The Exclusion Bill failed; on several occasions, Charles II dissolved Parliament because he feared that the bill might pass . After the dissolution of the Parliament of 1681, Charles ruled without a Parliament until his death in 1685 . When James succeeded Charles, he pursued a policy of offering religious tolerance to Roman Catholics, thereby drawing the ire of many of his Protestant subjects . Many opposed James's decisions to maintain a large standing army, to appoint Roman Catholics to high political and military offices, and to imprison Church of England clerics who challenged his policies . As a result, a group of Protestants known as the Immortal Seven invited James II's daughter Mary and her husband William III of Orange to depose the king . William obliged, arriving in England on 5 November 1688 to great public support . Faced with the defection of many of his Protestant officials, James fled the realm and William and Mary (rather than James II's Catholic son) were declared joint Sovereigns of England, Scotland and Ireland . </P>

Who was the only ruler of britain who ruled instead of a king or queen