who was Tamar in the Bible

Tamar was the daughter of King David who was lured and raped by Amnon, her step brother.

In the course of time, Amnon son of David fell in love with Tamar, the beautiful sister of Absalom son of David. 2 SAMUEL 13:1

The tragic rape of Tamar ruined an innocent girl’s life and upset the balance of power in Israel.
Tamar and Amnon were half siblings; they shared a common father (David) but different mothers. Over time, Amnon grew obsessed with Tamar, to the point where it began to affect his physical well-being.
With the aid of one of his advisers, Amnon concocted a plan to lure Tamar to his bedroom pretending to be ill, he duped the king into sending Tamar to him and he raped her.
Tamar protested, trying to persuade Amnon that his behavior would bring disaster on them both.
But Amnon was not to be deterred. Sadly, as so often happens when something (or someone) is unjustly taken by force, Amnon grew to despise Tamar almost immediately. The object of his obsession was now an object of revulsion. Tamar was humiliated, and her father, David, and full brother Absalom were enraged. However, David’s fury does not seem
to have materialized into action. While David fumed, Tamar took refuge in Absalom’s house, her future prospects ruined by Amnon’s lust.
When his father failed to defend Tamar’s honor, Absalom took matters into his own hands and conspired to kill his half brother Amnon. In doing so, he struck down David’s firstborn and presumed heir to the throne. Absalom, the third son of David, would eventually lose his own life, causing the throne to pass to Solomon.
The story of Tamar and Amnon bears a number of unfortunate parallels to the account of David’s own infidelity. In each case, the guilty party used an unwitting accomplice to fetch the victim. Just
as David had used Joab to summon Bathsheba’s ill-fated husband, so now David found himself the pawn in Amnon’s plan to rape Tamar. Also, just as David’s sin had resulted in the loss of a son,
now Amnon’s sin would lead to the death of not just one but two sons of David. Sometimes history has a tragic way of repeating itself.