Frederick Augustus III (German: Friedrich August III) (25 May 1865 – 18 February 1932) was the last King of Saxony (1904–1918) and a member of the House of Wettin.

Born in Dresden, Frederick Augustus was the son of King George of Saxony (1832-1904) and his wife Maria Anna, Infanta of Portugal (1843-1884). He was an older brother of Princess Maria Josepha of Saxony. His maternal first cousins included (among others) Carlos I of Portugal, Infante Afonso, Duke of Porto, Prince Wilhelm of Hohenzollern-Sigmaringen and Ferdinand I of Romania.

Frederick Augustus served in the Royal Saxon Army before becoming king, and later was promoted to Generalfeldmarschall. He abdicated as king on 13 November 1918, after the defeat of the German Empire in World War I. He died in Sibyllenort (Szczodre) in Lower Silesia and was buried in Dresden.

Frederick Augustus entered the Royal Saxon Army in 1877 as a second lieutenant, despite being only twelve years old. Given his royal status, he advanced rapidly through the ranks. He served initially with the Royal Saxon 1. (Leib-) Grenadier Regiment Nr. 100. He was promoted to first lieutenant in 1883, captain in 1887, major in 1889 and lieutenant colonel in 1891. By 1891, he was commander of the 1st Battalion of Schützen (Füsilier)-Regiment Nr. 108. He was promoted to colonel on 22 September 1892 and took command of the Schützen (Füsilier)-Regiment Nr. 108 on the same day. On 20 September 1894, the 29-year old prince was promoted to Generalmajor and given command of the 1st Royal Saxon Infantry Brigade Nr. 45 (Saxon higher units usually bore two numbers: one their Saxon Army number and the other their number in the Prussian Army order of battle). On 22 May 1898, he was promoted to Generalleutnant and given command of the 1st Royal Saxon Infantry Division Nr. 23. He commanded this division until 26 August 1902, when he took command of the XII (1st Royal Saxon) Corps. He was promoted to General der Infanterie one month later, on 24 September. He remained in command of the corps until October 1904, when he became king. His formal military career ended with his accession to the throne, but he was promoted subsequently to Generaloberst and then to Generalfeldmarschall (on 9 September 1912).

Frederick Augustus married Archduchess Luise, Princess of Tuscany, in Vienna on 21 November 1891. They were divorced in 1903 by the royal decree of the King after she ran away while pregnant with her last child. Luise's flight from Dresden was due to her father-in-law threatening to have her interned in Sonnestein Mental Asylum for life. Her brother supported her in her wish to escape Saxony. Emperor Franz-Josef of Austria-Hungary did not recognise the divorce. They had seven children.