William Morris Hughes (25 September 1862 – 28 October 1952) was an Australian politician who served as the seventh prime minister of Australia from 1915 to 1923. He led the nation during World War I, and his influence on national politics spanned several decades. He was a member of the federal parliament from the Federation of Australia in 1901 until his death in 1952, and is the only person to have served as a parliamentarian for more than 50 years. He represented six political parties during his career, leading five, outlasting four, and being expelled from three.

Hughes was born in London to Welsh parents. He emigrated to Australia at the age of 22, and became involved in the fledgling Australian labour movement. He was elected to the New South Wales Legislative Assembly in 1894, as a member of the New South Wales Labor Party, and then transferred to the new federal parliament in 1901. Hughes combined his early political career with part-time legal studies, and was called to the bar in 1903. He first entered cabinet in 1904, in the short-lived Watson government, and was later the Attorney-General of Australia in each of Andrew Fisher's governments. He was elected deputy leader of the Australian Labor Party in 1914.

Hughes became prime minister in October 1915, when Fisher retired due to ill health. The war was the dominant issue of the time, and his support for sending conscripted troops overseas caused a split within Labor ranks. Hughes and his supporters were expelled from the party in November 1916, but he was able to remain in power at the head of the new National Labor Party, which after a few months merged with the Liberals to form the Nationalist Party. His government was re-elected with large majorities at the 1917 and 1919 elections. Hughes established the forerunners of the Australian Federal Police and the CSIRO during the war, and also created a number of new state-owned enterprises to aid the post-war economy. He made a significant impression on other world leaders at the 1919 Paris Peace Conference, where he secured Australian control of the former German New Guinea.

At the 1922 Australian federal election, the Nationalists lost their majority in parliament and were forced to form a coalition with the Country Party. Hughes's resignation was the price for Country Party support, and he was succeeded as prime minister by Stanley Bruce. He became one of Bruce's leading critics over time, and in 1928, following a dispute over industrial relations, he and his supporters crossed the floor on a confidence motion and brought down the government. After a period as an independent, Hughes formed his own organisation, the Australian Party, which in 1931 merged into the new United Australia Party (UAP). He returned to cabinet in 1934, and became known for his prescient warnings against Japanese imperialism. As late as 1939, he missed out on a second stint as prime minister by only a handful of votes, losing the 1939 United Australia Party leadership election to Robert Menzies.

Hughes is generally acknowledged as one of the most influential Australian politicians of the 20th century. He was a controversial figure throughout his lifetime, and his legacy continues to be debated by historians. His strong views and abrasive manner meant he frequently made political enemies, often from within his own parties. Hughes's opponents accused him of engaging in authoritarianism and populism, as well as inflaming sectarianism; his use of the War Precautions Act 1914 was particularly controversial. His former colleagues in the Labor Party considered him a traitor, while conservatives were suspicious of what they viewed as his socialist economic policies. He was extremely popular among the general public, particularly ex-servicemen, who affectionately nicknamed him "the little digger".

Hughes was born on 25 September 1862, at 7 Moreton Place, Pimlico, London, the son of William Hughes and the former Jane Morris. His parents were both Welsh. His father, who worked as a carpenter and joiner at the Palace of Westminster, was from North Wales and was a fluent Welsh speaker. His mother, a domestic servant, was from the small village of Llansantffraid-ym-Mechain (near the English border), and spoke only English. Hughes was an only child; at the time of their marriage, in June 1861, his parents were both 37 years old.

Hughes's mother died in May 1869, when he was six years old. His father subsequently sent him to be raised by relatives in Wales. During the school term, he lived with his father's sister, Mary Hughes, who kept a boarding house in Llandudno named "Bryn Rosa". He earned pocket money by doing chores for his aunt's tenants and singing in the choir at the local church. Hughes began his formal education in Llandudno, attending two small single-teacher schools. He spent his holidays with his mother's family in Llansantffraid. There, he divided his time between "Winllan", the farm of his widowed aunt (Margaret Mason), and "Plas Bedw", the neighbouring farm of his grandparents (Peter and Jane Morris).

Hughes regarded his early years in Wales as the happiest time of his life. He was immensely proud of his Welsh identity, and he later became active in the Welsh Australian community, frequently speaking at Saint David's Day celebrations. Hughes called Welsh the "language of heaven", but his own grasp of it was patchy. Like many of his contemporaries, he had no formal schooling in Welsh, and had particular difficulties with spelling. Nonetheless, he received and replied to correspondence from Welsh-speakers throughout his political career, and as prime minister famously traded insults in Welsh with David Lloyd George.