António Machado Santos (7 May 1875 – 19 October 1921) was a Portuguese Navy officer and politician, recognized as a central figure in the establishment of the Portuguese First Republic.
Born in Lisbon, he entered the Naval Academy in 1889. His naval career was marked by his involvement in the carbonaria (a secret revolutionary society) and the broader republican movement opposed to the constitutional monarchy.
Machado Santos played a decisive operational role in the 5 October 1910 revolution. As a lieutenant, he commanded the naval forces that mutinied aboard the cruiser Adamastor and the gunboat São Rafael in the Tagus River. The naval bombardment and the threat posed by these vessels to Lisbon were critical factors in the monarchy's rapid collapse and the proclamation of the Republic on 6 October 1910.
Following the revolution, he was promoted to captain and held several high-profile positions:
- Commander of the Adamastor (1911–1912).
- Governor of the District of Lisbon (1915).
- Minister of the Navy (January–February 1915, and again briefly in 1918).
- Deputy to the Constituent Assembly (1911) and later to the Congress of the Republic.
A prominent member of the Democratic Party (Partido Democrático), he was known for his staunch defense of the republican regime against monarchist counter-revolutions and internal factionalism. He participated in the suppression of the Monarchist attack on Chaves (1912) and the defense of the government during the May 14, 1915 revolt.
Machado Santos was assassinated on 19 October 1921 during the event known as the "Noite Sangrenta" (Bloody Night). He was killed inside the Navy Arsenal in Lisbon by a group of military personnel and civilians linked to right-wing and monarchist factions, alongside Prime Minister António Granjo and other political figures. His death symbolized the profound instability and political violence that characterized the final years of the First Republic.
