Both King Saul and Mordechai were from the same family:
Shmuel I 1-2:
There was a man of Benjamin whose name was Kish son of Abiel son of Zeror son of Becorath son of Aphiah, a Benjaminite, a man of substance. He had a son whose name was Saul, an excellent young man; no one among the Israelites was handsomer than he; he was a head taller than any of the people.
In Shushan HaBira lived a Jew by the name of Mordecai, son of Yair son of Shimei son of Kish, a Benjaminite.
In the Haftara for Parshat Zachor, King Saul is given the task to fight Amalek and not take from the spoils:
Shmuel I 15:1-9:
Shmuel said to Saul, “I am the one the LORD sent to anoint you king over His people Israel. Therefore, listen to the LORD’s command! “Thus said the LORD of Hosts: I am exacting the penalty for what Amalek did to Israel, for the assault he made upon them on the road, on their way up from Egypt. Now go, attack Amalek, and destroy all that belongs to him. Spare no one, but kill alike men and women, infants and sucklings, oxen and sheep, camels and donkeys!” Saul mustered the troops and enrolled them at Telaim: 200,000 men on foot, and 10,000 men of Yehuda. Then Saul advanced as far as the city of Amalek and lay in wait in the wadi. Saul said to the Kenites, “Come, withdraw at once from among the Amalekites, that I may not destroy you along with them; for you showed kindness to all the Israelites when they left Egypt.” So the Kenites withdrew from among the Amalekites. Saul destroyed Amalek from Havilah all the way to Shur, which is close to Egypt, and he captured King Agag of Amalek alive. He destroyed all the people, putting them to the sword; but Saul and the troops spared Agag and the best of the sheep, the oxen, the second-born, the lambs, and all else that was of value. They would not destroy them; they destroyed only what was cheap and worthless.
Unfortunately, King Saul failed to complete the task of fighting Amalek.
Shmuel confronted Saul:
Shmuel I 15:14-15:
“What,” demanded Shmuel, “is this bleating of sheep in my ears, and the lowing of oxen that I hear?” Saul answered, “They were brought from the Amalekites, for the troops spared the choicest of the sheep and oxen for sacrificing to the LORD your God. And we destroyed the rest.”
King Saul did not follow directions. He did not fully destroy Amalek and he took their possessions.
In contrast, we see in Ester 8:11 that the Jewish people were permitted to take their enemies spoils during the war:
The king has permitted the Jews of every city to assemble and fight for their lives; if any people or province attacks them, they may destroy, massacre, and exterminate its armed force together with women and children, and plunder their possessions—
Yet we read in three places that the Jews did not take from the spoils:
…But they did not lay hands on the spoils.
And the Jews in Shushan mustered again on the fourteenth day of Adar and slew three hundred men in Shushan. But they did not lay hands on the spoil. The rest of the Jews, those in the king’s provinces, likewise mustered and fought for their lives. They disposed of their enemies, killing seventy-five thousand of their foes; but they did not lay hands on the spoils.
We see from here that although Mordechai and the Jews of his generation were permitted to take from the spoils, they did not. They corrected King Saul’s transgression in their war against Haman, a descendent of King Agag, a descendant of Amalek.