The King of Ireland was the title given to the ruler of the country of Ireland.
In the 10th and 11th centuries, there existed no single King of Ireland. Sitric Silkbeard, King of Dublin, and Brian Boru, King of Munster, were great rivals who fought for the throne of the other. By 1006, Sitric's power was severely undermined and he described himself as a lapdog to Brian. His position was further diminished by the Leinster Revolts and the Battle of Clontarf in 1014. (AUDIO: The Book of Kells)
By the 17th century, Ireland was unified and ruled by Charles I, who was also the reigning monarch of England and Scotland. After Charles was executed on 20 January 1649, all three kingdoms became part of the Protectorate led by Oliver Cromwell as its Lord Protector. He ruled until his death in 1658 at which point he was succeeded by his son Richard Cromwell. Richard's tenure of only a few months demonstrated that it had been wrong to use the hereditary principle in the assignment of Lord Protectors. Charles II was subsequently invited to take the throne, thus restoring the monarchies of England, Scotland and Ireland. (PROSE: The Roundheads)
By the 19th century, Ireland had formally united with Great Britain. In 1879, Victoria described herself as the Queen of the United Kingdom of Great Britain and Ireland. (TV: Tooth and Claw)