The Qur'an informs us that Karun was the owner of great possessions in Egypt despite being a descendant of the Israelite tribe.
In the following verse Allah indicates that Karun opposed the Prophet Moses (pbuh) together with Pharaoh:
We sent Moses with Our Signs and clear authority to Pharaoh, Haman and Karun. But they said, "A lying magician." (Surah Ghafir: 23-24)
It is noteworthy that Karun, who was with Pharaoh, was also in charge of a great treasure
Karun was one of the people of Moses but he lorded it over them. We gave him treasures, the keys alone to which were a heavy weight for a party of strong men… (Surat al-Qasas: 76)
The great fortune and status Karun possessed in Egypt, due to his closeness to Pharaoh, made him arrogant and insolent towards his own people. He refused to accept the Prophet Moses' (pbuh) message, and boasted about his possessions to make the Children of Israel feel attachment to the life of this world. In fact, his great fortune and status became the envy of some of the people from the Prophet Moses' (pbuh) tribe. Allah relates the arrogance of Karun and the envy those of poor faith among the Children of Israel felt for him:
He went out among his people in his finery. Those who desired the life of the world said, "Oh! If only we had the same as Karun has been given! What immense good fortune he possesses." (Surat al-Qasas: 79)
The true believers among the Children of Israel never felt inclined towards Karun. On the contrary, they comprehended the pitiful situation he was in, and warned him:
…When his people said to him, "Do not gloat. Allah does not love people who gloat. Seek the abode of the Hereafter with what Allah has given you, without forgetting your portion of the world. And do good as Allah has been good to you. And do not seek to cause corruption in the earth. Allah does not love corrupters." (Surat al-Qasas: 76-77)
These same people of faith gave advise to some of the members of their own tribe who were inclined to Qarun, and warned them to retain the nobility of a believer in their conduct, and never to prefer the temporary pleasures of this world over the mercy of Allah:
...Those who desired the life of the world said, "Oh! If only we had the same as Karun has been given! What immense good fortune he possesses." But those who had been given knowledge said, "Woe to you! Allah's reward is better for those who believe and act rightly. But only the steadfast will obtain it." (Surat al-Qasas: 79-80)
The main reason why Karun went astray was his belief that he was possessed with "knowledge." In other words, he had the boastful attitude that he was superior to other people.
He said, "I have only been given it because of knowledge I have." Did he not know that before him Allah had destroyed generations with far greater strength than his and far more possessions? The evildoers will not be questioned about their sins. (Surat al-Qasas: 78)
Ultimately, the prepared end for Pharaoh and Haman, was the same met by Karun: