Joab son of Zeruiah יואב בן צרויה

Joab was the son of Zeruiah, David's sister, the eldest of three brothers. He took the stronghold of Zion for the king and became head of the army for it. After that every war of the reign went through him.

He is also the executor of the worst. The letter about Uriah, which David sent by Uriah's own hand, was carried out by Joab: he set him where the fighting was fiercest and drew his own men back. Abner, who had come in peace, he stabbed at the gate of Hebron. Absalom, hanging in the branches, he killed with three darts, though the king had asked in everyone's hearing that the young man be spared — and it was he who then came to the weeping David and said, roughly and to the point: get up and speak to the people, or by morning you will have no one left.

Amasa, appointed in his place, he took by the beard with his right hand as if to kiss him, and struck.

In his last days David named it outright: he shed the blood of war in peacetime. Joab backed Adonijah — and lost. He fled to the Tent and took hold of the horns of the altar; Solomon ordered Benaiah to kill him there, at the altar itself, and Benaiah did it.

Scripture's verdict is double and never reduced to one line: without Joab there would have been no kingdom of David, and with Joab it was permanently in blood.