As a Christian name, Ruth has been in use since the Protestant Reformation. In England it was associated with the archaic word ruth meaning "pity, compassion" (now only commonly seen in the word ruthless). The name became very popular in America following the birth of "Baby" Ruth Cleveland (1891-1904), the daughter of President Grover Cleveland.
This name has been used occasionally in England since the 12th century. It was not common in the English-speaking world until the end of the 20th century.
Despite this potentially negative association, the name was occasionally used by Christians during the Middle Ages. In the English-speaking world both Eve and the Latin form Eva were revived in the 19th century, with the latter being more common.