Samaritan n.

Old English, "native or inhabitant of Samaria," a district of ancient Palestine, from Late Latin Samaritanus, from Greek Samareitēs, from Samareia (see Samaria). A non-Hebrew race was settled in its cities by the king of Assyria after the removal of the Israelites from the country. 

Originally idolaters they soon began to worship Jehovah, but without abandoning their former gods. They afterward became monotheists, and observed the Mosaic law very strictly, but with peculiar variations. About 400 B. C. they built a temple on Mount Gerisim, which was destroyed 130 B. C. They began to decline toward the close of the fifth century after Christ. They still exist, bat are nearly extinct. [Century Dictionary, 1897]

The figurative use for "charitable or benevolent person," with reference to the Biblical story of the good Samaritan in Luke x, is attested from 1630s. As an adjective by late 14c. Related: Samaritanism.