The story of Adam and Iblis 

 After creation of Adam  Allah, Almighty, said to the angels prostrate yourselves before Adam, they all prostrate except Iblis. Although the prostration was before Adam, but the obedience was to Allah. Iblis refused and was arrogant (proud) and became one of the disbelievers.

 When Allah commanded the angels to prostrate before Adam, Iblis was not an angel for Allah Azza wa Galla said: "Except Iblis (Satan), he was one of the jinn, he disobeyed the command of His lord" (Alkahf:50), but he was trying to imitate behavior and deeds of the angels. And when superior creatures like the Angels were commanded to prostrate and show their respect for Adam, the Jinn must have been ordered without saying to do the same.

Why Iblis disobeyed the command of Allah?.

 When Allah Asked Iblis" what prevented you from prostrating when I commanded you (to prostrate with those who prostrate)? Iblis (Satan) said: I would never prostrate to a human being whom you created out of clay from an altered black mud (decayed mud), I am better than he (human being) you created me from fire whereas you created him from clay.

 Here Iblis made a false comparison when he looked at the origin of creation, and he saw that the better one can not prostrate to he who is less. He did not obey Allah because that comparison, and because he ignored the honor bestowed that Allah created Adam with his hands and blowing life into him,  and thus he was out of Allah's mercy and lost hope of acquiring Allah's mercy. 

 Iblis became an infidel because he had challenged Allah's commandment, then Allah said to him "go down from it, for it is not for you to be arrogant (behave proudly) therein, so get out, indeed, you are of the disgraced ones (debased)".