Martim Moniz de Ribadouro

Statue of Martín Muñoz, last Count of Coimbra (before integration in County of Portucale). In Puente de San Pablo, Burgos

Martín Muñoz de Montemayor (; before 1080 - after 1111), also known as Martín Muñoz de Ribadouro, was a medieval noble from the County of Portugal who, through marriage, became the son-in-law of the famous alvazil Sisnando Davides. Sisnando appointed him as alvazil, and after his death, Martín became the new Count of Coimbra. He was later deposed and nominated Governor of Arouca, possibly relatives of the governor, considering at least the similar patronymic of the first two.

Thus, the death of alvazil Sesnando Davides, Martín's father-in-law, on December 25, 1091, did not mark the immediate end of Mozarabic administration in Coimbra, which had been in place since 1064, the year of the city's reconquest by Ferdinand the Great (likely motivated by Sesnando himself).

However, the actions of Alfonso VI of León and Castile were not peaceful. Likely wishing to reduce Mozarabic influence over Coimbra, he did not delay: even before the death of the alvazil, at Easter 1091, he appointed a new bishop for the city: Bishop Crescónio, who had been Abbot of Tui, and was recognized by all as the monarch's choice for the spiritual governance of Coimbra. However, the consecration and installation of the new bishop could only take place after the alvazil's death, during Martín Muñoz's government.

Conquests of Lisbon, Santarém, and Sintra Around that time, Alfonso VI was also negotiating with Omar al-Mutawakkil the handover of the cities then under Arab control - Lisbon, Santarém, and Sintra - and planned to strengthen the administrative and military posts of these newly acquired frontier cities.

Martín Muñoz likely died shortly after 1111, as he did not confirm any documents after that date.