Ruth was a Moabitess, who married Mahlon, the son of Elimelech and Naomi, but Elimelech and his two sons died.
When Naomi decided to return to Bethlehem, Ruth went with her, and although Orpah, Naomi's other -in-law went back home, said Entreat me not to leave thee, or to return from following after thee: for whither thou goest, I will go; and where thou lodgest, I will lodge: thy people shall be my people, and thy God my God: Where thou diest, will I die, and there will I be buried: the LORD do so to me, and more also, if ought but death part thee and me.
(Ruth 1:16-17, KJV) Ruth went to glean in the fields, where she met Boaz. At the instigation of Naomi she seduces Boaz by night; Boaz indicates his desire to marry her, and calls Ruth a "woman of noble character".
After overcoming the obstacle of having a relative with a prior claim, Boaz married Ruth, and they have a son, named Obed. The genealogy in the final chapter of the book explains how Ruth became the great-grandmother of David. She is also thus the ancestor of Joseph (husband of Mary and would-be father of Jesus), and is one of the five women mentioned in the genealogy of Matthew 1 (The others are Tamar, Rahab, Bathsheba, and Mary)