Shaytan – worst disbeliever
Allah answers this question by Himself:
وَإِذْ قُلْنَا لِلْمَلَـٰٓئِكَةِ ٱسْجُدُوا۟ لِـَٔادَمَ فَسَجَدُوٓا۟ إِلَّآ إِبْلِيسَ أَبَىٰ وَٱسْتَكْبَرَ وَكَانَ مِنَ ٱلْكَـٰفِرِينَ
“And remember when We said to the angels, “Prostrate before Adam,” so they all did—but not Iblis, who refused and acted arrogantly, becoming unfaithful.”
Chapter 2 (Surah Al-Baqarah) verse 34
So, the Shaytan showed pride, and indeed he was from the disbelievers. In fact, Allah says, ٱلشَّيَـٰطِينِ ۖ وَكَانَ ٱلشَّيْطَـٰنُ لِرَبِّهِۦ كَفُورًۭا. “And the Devil is ever ungrateful to his Lord.” [1] So, Shaytan showed extreme disbelief and extreme arrogance. And Shaytan is not just a disbeliever; he is the worst disbeliever. But if Shaytan believes in Allah, then what technically makes him a disbeliever?
Well, first and foremost, there are different levels of disbelief, and there are different ways to reject. Kufr really means to reject.
The disbelievers of Mecca
The disbelievers in Mecca, they didn’t deny Allah’s existence. In fact, Allah says if you were to ask them who created the heavens and the Earth, they would say it’s Allah [2]. So they had no problem acknowledging that Allah created the heavens and the Earth, but they associated partners with Allah, so they had a different type of kufr. They diluted and corrupted the religion of Abraham, and they added elements of shirk (associating partners with Allah—polytheism). There wasn’t a denial of Allah, but there was a deficiency in them in the way that they viewed Allah to a point that it became disbelief and polytheism.