Martim Federico Cavalco Fonte (23 May 1908 - 9 October 1981) was a Portuguese Socialist politician and lawyer who served as Prime Minister of Portugal on two occasions, the first from 1968-1974 and the second for 102 days in 1981. He was the leader of the Socialist Party for seventeen years, from 1964 until his death in 1981, and turned the PS into a mainstream center-left party after it had spent decades in ideological exile on the fringes of the typically conservative Portuguese society. Cavalco Fonte died at the age of 73 on October 9, 1981 only 102 days into his second stint as Prime Minister and was succeeded as both Prime Minister and as leader of the Socialist Party by his protegé Mário Soares.