Ferdinand Foch ( FOSH, French: [fɛʁdinɑ̃ fɔʃ]; 2 October 1851 – 20 March 1929) was a French general and military theorist who served as the Supreme Allied Commander during the First World War. An aggressive, even reckless commander at the First Marne, Flanders and Artois campaigns of 1914–1916, Foch became the Allied Commander-in-Chief in late March 1918 in the face of the all-out German spring offensive, which pushed the Allies back using fresh soldiers and new tactics that trenches could not withstand. He successfully coordinated the French, British and American efforts into a coherent whole, deftly handling his strategic reserves. He stopped the German offensive and launched a war-winning counterattack. In November 1918, Marshal Foch accepted the German cessation of hostilities and was present at the Armistice of 11 November 1918.

At the outbreak of war in August 1914, Foch's XX Corps participated in the brief invasion of Germany before retreating in the face of a German counter-attack and successfully blocking the Germans short of Nancy. Ordered west to defend Paris, Foch's prestige soared as a result of the victory at the Marne, for which he was widely credited as a chief protagonist while commanding the French Ninth Army. He was then promoted again to assistant commander-in-chief for the Northern Zone, a role which evolved into command of Army Group North, and in which role he was required to cooperate with the British forces at Ypres and the Somme. At the end of 1916, partly owing to the disappointing results of the latter offensive and partly owing to wartime political rivalries, Foch was transferred to Italy. Foch was appointed "Commander-in-Chief of the Allied Armies" on 26 March 1918 following being the commander-in-chief of Western Front with the title Généralissime in 1918. He played a decisive role in halting a renewed German advance on Paris in the Second Battle of the Marne, after which he was promoted to Marshal of France. Addington says, "to a large extent the final Allied strategy which won the war on land in Western Europe in 1918 was Foch's alone."

On 11 November 1918, Foch accepted the German request for an armistice. Foch advocated peace terms that would make Germany unable to pose a threat to France ever again. He considered the Treaty of Versailles too lenient on Germany. Winston Churchill attributed this famous quote about the Peace Treaty of Versailles to Foch: "This is not Peace. It is an Armistice for twenty years."