Sidónio Bernardino Cardoso da Silva Pais (Portuguese pronunciation: [siˈdɔniu ˈpajʃ]; 1 May 1872, in Caminha – 14 December 1918, in Lisbon) was a Portuguese military leader politician and diplomat, the fourth President in 1918. He was known as the President-King. On 5 December 1917, he led an uprising against Afonso Costa's Democratic Party government, and established an authoritarian regime and was elected President (unopposed) on 28 April 1918. He was murdered in central Lisbon, 11 days before Christmas 1918.
He was the eldest child and son of Sidónio Alberto Marrocos Pais (Caminha, Nossa Senhora da Assunção, 1 November 1846 – Ferreira do Zêzere, Dornes, 27 August 1883), a Law Clerk and Public Notary in Caminha and later in Pedrógão Grande and Sertã of Barcelos New Christian Jewish ancestry (on his great-great-grandfather António Velho da Fonseca), and wife (m. Caminha, Nossa Senhora da Assunção, 22 June 1871) Rita Júlia Cardoso da Silva (Caminha, Caminha, 29 August 1844 – Caminha, Caminha, 9 March 1919). His brothers and sisters were Rita (b. Caminha, Caminha, 1873), Alberto (Caminha, Caminha, 1874 – Caminha, Caminha, 1877), António (Caminha, Caminha, 15 November 1876 – Lisbon, Hospital da Marinha, 27 June 1949), who was also a military and married at the Igreja Matriz de Caminha, Caminha, 7 May 1904 Júlia Cândida de Sant' Ana Cerqueira (Caminha, Caminha, 1 September 1881 – Lisbon, 6 June 1968) and had issue, Ana da Glória (b. Caminha, Caminha, 1878), Alberto (b. Pedrógão Grande, 1881, d. child) and Aureliano (b. Sertã, 1883, d. child).