Sidónio Bernardino Cardoso da Silva Pais (Coimbra, 1 May 1872 - Lisbon, 14 December 1918), was a Portuguese politician, President in 1918. He was known as the President-King.

He was an army officer and taught Mathematics at the Army school, and later, at the University of Coimbra. He became a member of Parliament in 1911, and would be Minister of Finance for a short period. He was ambassador in Berlin from 1912 until 1916, when Portugal joined the First World War on the Allied side. He was a Germanophile.

On December 5 1917, he led a coup d'état, and imposed an authoritorian regime. He was proclaimed President two weeks later, and elected on direct elections on April 28 1918.

His short period in office has seen a warming of Church-State relations, the extension of the electoral franchise, and the smashing defeat of the ill-prepared Portuguese troops at La Lys , in France.

He escaped a first assassination attempt, but was shot on December 14 1918, at Rossio railway station, in Lisbon, when he was preparing to board a train to Oporto, in order to quell a rebellion.