Casto Plasencia y Maestro (17 July 1846 – 18 May 1890) was a Spanish painter of landscapes, portraits and murals.

[1] After becoming established in Madrid, he was chosen to do portraits of King Alfonso XII and Queen María.

As the Assistant Manager on a project at the San Francisco el Grande Basilica, he participated in decorating the main cupola[2] and was in charge of the paintings for the chapel of the Order of Carlos III.

In the summer of 1884, his fellow painter Tomás García Sampedro invited him to visit Muros del Nalón in Asturias.

He was charmed by the area and continued to visit there every summer with other painters and students who formed what came to be known as the "Colonia artística de Muros [es]", a group devoted to plein-air painting in the surrounding countryside.