He was the son of the first elector of Hanover, Ernest Augustus (1629–1698), and his wife Sophia who was a granddaughter of James I of England. He was heir through his father to the hereditary lay bishopric of Osnabrück and the duchy of Calenberg, which was one part of the Hanoverian possessions of the house of Brunswick. He acquired the other part by his marriage in 1682 to his cousin Sophia Dorothea of Celle. They had two children George (who later became George II) and Sophia (who married Frederick William of Prussia in 1706 and was the mother of Frederick the Great).
It was not a happy marriage. George had several mistresses, and his wife Sophia eloped with Swedish Count Philip Konigsmark who in 1694 mysteriously disappeared believed killed with George’s connivance and his body thrown in a river. Sophia was imprisoned in Castle Ahlden in Celle where she remained until she died 30 years later. In England Queen Anne had no surviving children and in 1701 Parliament passed the Act of Settlement to ensure a Protestant line of succession and oppose the claim of the Catholic James Edward Stuart. George’s mother Sophia became heiress to the British throne, but she died in May 1714 a few weeks before Queen Anne so when Anne died in August that year George became King George I of England and Scotland.
George arrived in England aged 54 speaking only a few words of English, with 18 cooks and two mistresses one very fat and the other thin and tall who became nicknamed ‘Elephant and Castle’ after an area in London. In Hanover he was absolute ruler but in England found that he had to work with Parliament and his Whig ministers particularly Lord Townshend who was dismissed, Earl Stanhope and Robert Walpole. The king grew frustrated in his attempts to control Parliament and more and more dependent upon his advisers as scandal surrounded him; his supporters turned against him, demanding freedom of action as the price of reconciliation. George rarely attended meetings with his ministers, and particularly Walpole became powerful and effectively Britain’s first Prime Minister.
Jacobite rebellions in Scotland in 1715 led by Lord Mar, and in 1719 supported by Spanish troops intending to place James Edward Stuart (‘The old Pretender’) on throne found little support and were quickly defeated. The ‘South Sea Bubble’ in which shares in companies were purchased in rash financial speculation before a stock market crash in 1720 left many investors ruined, and George was implicated in the scandal. Walpole’s management of the crisis by rescheduling debts and paying compensation using Government money helped return financial stability. George quarrelled with his son George (a trait inherited by successive Hanoverian kings) and became increasingly unpopular. He spent more and more time in Hanover where he died of a stroke in 1727 (Royal family history: www.britroyals.com)
Imprisoned his wife for life upon their divorce (The concise dictionary of national biography. Part 1 : from the beginnings till 1900. London : Oxford University Press, 1969, pg. 485).