Who was Tamar?
Tamar was the wife of Er, the oldest son of Judah (Gen 38:6 ff).
Upon her husband's death under the displeasure of Yahweh, his brother Onan ought to have performed the husband's part, but he evaded his duty in this respect, and likewise perished.
Shelah, the next brother, was promised to her, but not given. This led Tamar to the extraordinary course narrated in Gen 38:13 ff.
By her father-in-law she became the mother of Perez and Zerah (the King James Version "Pharez and Zarah").
Judah, who at first condemned her to be burned (Gen 38:24), was compelled to vindicate her (Gen 38:25,26). Through Perez she became an ancestress of Jesus (Grk: Thamar, Mt 1:3).
IBSE, "Tamar" (in the public domain) with minor edits.