Is Iblis (Satan) an angel or a Jinni?
And are the Jinn (creatures created from fire) his offspring or were he and his offspring created from them?
Iblis is one of the Jinn as Allah (Exalted be He) says:
And (remember) when We said to the angels: "Prostrate yourselves unto Adam." So they prostrated themselves except Iblîs (Satan). He was one of the jinn; he disobeyed the Command of his Lord.
He is not an angel. Moreover, he was created from fire while angels were created from light. This is mentioned in the Ayahs (Qur'anic Verses) talking about the creation of Iblis. Besides, this is proven in the Hadith of the Messenger of Allah (peace be upon him) narrated by
`Aishah (may Allah be pleased with her) in which he said:
Angels were created from light, Jinn were created from a smokeless flame of fire, and Adam was created from that which you have been told (i.e., sounding clay like the clay of pottery)
Imam Muslim in his Sahih.May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.