was the Duke of Devonshire (served 1756–1757); the most recent is John Major (served 1990–1997). Wealth After being appointed prime minister by King Charles III on 25 October 2022, Rishi Sunak became the richest prime minister ever, with an estimated combined personal fortune with his wife of £730 million. The previous richest prime minister was Lord Derby, with a personal fortune of over £7 million (about £444 million in today's money). The poorest prime minister was William Pitt the Younger, who was £40,000 (now over £1 million) in debt by 1800. Legal issues Before becoming prime minister, Robert Walpole was impeached and convicted in 1712 for "a high breach of trust and notorious corruption" and sentenced to six months imprisonment in the Tower of London. In 2006 and 2007, Tony Blair became the first sitting prime minister to be questioned as part of a criminal investigation, following the Cash-for-Honours scandal, but this was not under caution. In 2022, Boris Johnson received a fixed-penalty notice relating to violations of the COVID-19 lockdown regulations in the Partygate scandal, becoming the first prime minister found to have broken the law in office. Future prime minister Rishi Sunak, then Chancellor of the Exchequer, was also fined at the same time. In January 2023, during his current period in office, Rishi Sunak was issued a fixed penalty notice by Lancashire Police for failing to wear a seatbelt in his ministerial car while filming an Instagram video to promote his government's levelling up policy. Sunak hence became the second prime minister in history to be found to have broken the law in office. Female There have been three female prime ministers, all Conservative. They have led the United Kingdom for a total of . Margaret Thatcher — served May 1979–November 1990, . Theresa May — served July 2016–July 2019, . Liz Truss — served September–October 2022, . Since Cameron's 2010 appointment through to Sunak's in 2022, male and female prime ministers have alternated. Birthplace Two prime ministers were born in Ireland, both in Dublin in the Kingdom of Ireland before the Act of Union of 1801. Lord Shelburne — born in Dublin in 1737 The Duke of Wellington — born at 6 Merrion Street, Dublin, in 1769 Two further prime ministers were born outside of the British Isles. Bonar Law — born in the colony of New Brunswick in what is now Canada, the first prime