Iblis and other jinn, and humans, have free will and freedom of choice, to obey Allah or to disobey Him, as Allah says (interpretation of the meaning): 

“Then whosoever wills, let him believe; and whosoever wills, let him disbelieve.” [18:29] 

“Verily, We showed him the way, whether he be grateful or ungrateful.” [76:3] 

Allah commanded Iblis to prostrate to Adam (peace be upon him), but he refused and was arrogant, and was one of the kafirs (disbelievers). So Allah expelled him from His mercy, and cursed him until the Day of Judgement. 

Allah says (interpretation of the meaning): 

“And (remember) when We said to the angels: ‘Prostrate yourselves before Adam.’ And they prostrated except Iblis (Satan), he refused and was proud and was one of the disbelievers (disobedient to Allah).” [2:34] 

“So the angels prostrated themselves, all of them together.

Except Iblis (Satan) — he refused to be among the prostrators.

(Allah) said: ‘O Iblis (Satan)! What is your reason for not being among the prostrators?’

[Iblis] said: ‘I am not the one to prostrate myself to a human being, whom You created from dried (sounding) clay of altered mud.’

(Allah) said: ‘Then, get out from here, for verily, you are Rajeem (an outcast or a cursed one).

And verily, the curse shall be upon you till the Day of Recompense (i.e. the Day of Resurrection).” [15:30-35] 

Then Iblis asked for a respite until the Day of Resurrection, and Allah granted him that. 

Allah says (interpretation of the meaning): 

“[Iblis] said: ‘O my Lord! Give me then respite till the Day they (the dead) will be resurrected.’

Allah said: ‘Then verily, you are of those reprieved,

Till the Day of the time appointed.’” [15:36-38] 

When Iblis was certain that he is one of those who are doomed, as well as his being arrogant and being ungrateful to his Lord, he resolved to mislead whomever he could of the slaves of Allah, so that they would be with him in Hell. 

Allah says (interpretation of the meaning): 

“[Iblis] said: ‘O my Lord! Because You misled me, I shall indeed adorn the path of error for them (mankind) on the earth, and I shall mislead them all.

Except Your chosen, (guided) slaves among them.’” [15:39, 40] 

He is eager to mislead and corrupt, so as to increase the numbers of his followers and worshippers among the doomed who will share his fate.  

Iblis knows that his destination is the Fire, and he hopes to take everyone else with him to Hell, out of envy, hatred, kufr (disbelief) and stubbornness. 

He hates mankind, who are the children of Adam (peace be upon him), and he is hostile towards them because he is cursed and has been banished from the mercy of Allah because of his refusal to prostrate to their father Adam (peace be upon him). Hence Allah has warned His slaves against him and has said (what means): 

“Surely, Shaytan (Satan) is an enemy to you, so take (treat) him as an enemy. He only invites his hizb (followers) that they may become the dwellers of the blazing Fire.” [35:6] 

Iblis does not need anyone to whisper to him, because he is the source of all evil. 

The believer can be saved from his plots and traps by obeying his Lord and adhering to His religion, for the shaytaan has no power over those who believe, as Allah says (interpretation of the meaning): 

“So when you want to recite the Quran, seek refuge with Allah from shaytan, the outcast (the cursed one).

Verily, he has no power over those who believe and put their trust only in their Lord (Allah).

His power is only over those who obey and follow him (Satan), and those who join partners with Him (Allah, i.e. those who are mushrikoon, i.e., polytheists).” [16:98-100] 

And Allah knows best.