The answer is: Samuel

1 Samuel 15:32-33 - Samuel completed the job that Saul failed to do

In the dramatic narrative of 1 Samuel, the clash between Samuel and Agag unfolds against a backdrop of divine command and human failure. Saul, Israel's first king, was given a clear mandate to eliminate the Amalekites, a people whose sins—especially their cruelty—had reached a point of divine judgment. Transgressing this command weakened Saul's kingship and ultimately saw him rejected by God.

Enter Samuel, the prophet who wasn't just a mouthpiece for divine instruction but a fierce enforcer of God's will. After Saul spared Agag, the Amalekite king, Samuel took matters into his own hands, executing Agag himself. This moment encapsulates an important theme of this text: accountability. Saul's unwillingness to fully comply with God's command led to dire consequences, underscoring that partial obedience isn't sufficient in spiritual matters.

Interestingly, the tradition holds that Samuel is not only a prophet but also a judge and psalmist; he plays a pivotal role in the lead-up to Israel's monarchy. Samuel's involvement in Agag's demise conveys the seriousness of tackling sin head-on—it wasn’t enough to just wage war; internal evil must be eradicated fully and decisively.

Moreover, this story hints at the deeper meaning of prophecy and leadership and how new generations often emerge from the failures of the past to set things right. Samuel’s decisive action echoes through scripture, emphasizing fidelity to God’s directions—an enduring reminder that the road to redemption often requires making tough choices.