Is Iblis an Angel?

Question:

Is Iblis, may Allah curse him, an angel or from other than them? And if he is from other than them what is the type of seclusion in Allah's Words:
All the angels prostrated themselves, except Iblis."

Answer:

It should be known that the angels are creatures of Allah. He created them from light, they never disobey Him, and do as He says. As for Iblis (Satan), Allah mentioned that he was amongst the Jinn, Allah says:
"... and when We said to the angels, prostrate yourselves to Adam, they all did, except Iblis who was from the Jinn, who transgressed the command of his Lord".

Allah mentions in the Qur'an what Iblis said when He commanded him to prostrate himself to Adam. He said:
"You created me from Fire, and You created him from clay".

As for the type of seclusion, in His Words :
"All the angels prostrated themselves, except Iblis".

It is a separate seclusion, as one may say: "Everyone came except for a donkey." There are some people of knowledge who say Iblis, may Allah curse him, is an angel, except that he disobeyed Allah, the Exalted, and insisted on being disobedient. Iblis deserved the curse of Allah till the Day of Requital.

Source:
Fatawa Islamiyah, Vol. 1 Pages 96-97