According to Islam there are 3 races with a higher intelligence. Angels, Jinns, and Humans. Jinns and Humans have free will, meaning they can choose to go against God and nature. Angels have no free will, they are in complete balance with God and nature and cannot choose to be otherwise.
Iblis was one of the greatest Jinns who use to be loyal to God, but when Humans were created, he believed that he was a higher being than humans, therefore he chose to go against God and therefore his greatest crime was pride.
The Qur'an portrays Iblis, or Satan, as a jinn. The Qur'an says: "Call to mind, when We commanded the angels, submit to Adam, they all submitted, but Iblis did not; he refused and was arrogant." Submit does not necessarily mean to bow down or worship. When we submit to a higher authority, that is not the same thing as worship.
I found this explanation from a Muslim: Satan never repented to God not only this but Satan also argued and challenged God, while Adam repented to God so God forgave him. God says in the Quran:
( 38-74 ) Except Iblees; he was arrogant and became among the disbelievers.
( 7-14 ) [Satan] said, "Reprieve me until the Day they are resurrected."
( 7-15 ) [Allah] said, "Indeed, you are of those reprieved."
( 7-16 ) [Satan] said, "Because You have put me in error, I will surely sit in wait for them on Your straight path.
( 7-17 ) Then I will come to them from before them and from behind them and on their right and on their left, and You will not find most of them grateful [to You]."
( 7-18 ) [Allah] said, "Get out of Paradise, reproached and expelled. Whoever follows you among them - I will surely fill Hell with you, all together."