Why was Satan named Iblees?

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah and that Muhammad is His slave and Messenger.

Iblees (Satan) is the father of the jinn, just as Aadam (Adam)  is the father of mankind. Whoever rebels against His Lord and disobeys him is called a shaytaan (devil; literally means rebellious) regardless of whether he is from the jinn or is human. Shaykhul-Islam Ibn Taymiyyah wrote, "The shayaateen (plural of Shaytaan) are the rebellious and disobedient ones from among the Jinn and mankind; and all the Jinn are the offspring of Iblees."

The Arabic word 'Iblees' is derived from the noun 'Iblaas', which means despair, remorse, and grief. Allaah, The Exalted, says (what means): {...and they were (then) mublisoon (in despair).} [Quran 6:44] The Arabic word 'mublisoon' used in the verse means 'to be in a state of despair, remorse, and grief.'

The father of the jinn was named Iblees because he despaired from the Mercy of Allaah, The Exalted. Ibn Katheer wrote, "Allaah named him 'Iblees' symbolizing that he 'ablasa min rahmat-illah' (despaired of the Mercy of Allaah; that there was no hope for him of mercy)." [Tafseer Ibn Katheer]

Allaah knows best.