The title given to the great adversary of God and all humans. Before the creation of the world Lucifer was God's most highly esteemed Angel. Then, due to selfish ambition, Satan rebelled against God and 1/3 of God's Angels followed after him.
Satan is also referred to as the "devil" which means slanderer or false accuser. He is also referred to as; "the tempter" in 1 Thessalonians 3:5; "Beelzebub" in Matthew 12:24; "the wicked one" in Matthew 13:19, 38; "the ruler of this world" in John 12:31; "the god of this age" in 2 Corinthians 4:4; "Belial" in 2 Corinthians 6:15; "the prince of the power of the air" in Ephesians 2:2; and "the accuser of our brethren" in Revelation 12:10.
In Job chapters 1 and 2 we learn a lot about Satan's relationship with God:
Job 1:6 when the Angels go before God "... and Satan also came with them." Obviously indicating that Satan can go up to God only when accompanied by other Angels.
Job 1:7 thru 11 we see that God and Satan have a conversation.
Job 1:12 Satan is given a limitation "... everything he has is in your hands, but on the man himself do not lay a finger. ..."
Job 2:3 further emphasizes God's responsibility even though it was Satan that did the evil deed "... though you incited me against him to ruin him without any reason."
Finally there is the bottom line from Job after his wife tries to persuade him to rebel against God in Job 2:10 "... Shall we accept good from God, and not trouble?"
In Job (primarily Job 1:8 - 2:10) we learn that Satan does nothing without God's permission and/or restrictions. With the temptation of Jesus in the wilderness for 40 days (Luke 4:1-13) Jesus refutes Satan at every corner. With that said, though, God's Word also gives us a picture of Satan's allowed realm in Ephesians 6:12 "For our struggle is not against flesh and blood, but against the rulers, against the authorities, against the powers of this dark world and against the spiritual forces of evil in the heavenly realms."
The following are additional aspects of Satan:
John 12:31 "... prince of this world ..."
Matthew 13:38-39 "...The weeds are the sons of the evil one, 39 and the enemy who sows them is the devil...."
As for us humans God's Word gives us 4 features that will keep Satan's power away from us:
Those of us that are Born again Christians can never be possessed by Satan since we have God in us [refer to "Demon Possession"].
Secondly, as Born again Christians, we have a guardian Angel that looks over us [refer to "Angels"].
Third, through the Apostle Paul, God assures us that we cannot be tempted beyond what we can handle (1 Corinthians 10:13 "No temptation has seized you except what is common to man. And God is faithful; he will not let you be tempted beyond what you can bear. ...").
And, finally, if we are ever tempted, God will always give us a way out (1 Corinthians 10:13 "... But when you are tempted, he will also provide a way out so that you can stand up under it.").
The media seems to always portray Satan as a red human figure with horns and a tail. This portrayal seems to make him seem more human than as an evil angelic being.
Lucifer was created by God, was God's highest in authority Cherubim Angel and yet rebelled against God and took 1/3 of God's created Angels with him in the rebellion. Lucifer, who then becomes Satan or the Devil, is cast down to earth with the third of his fallen angel fallers. The devil and his demons are the darkness while God is the light. They hate God and all humans. Their final destiny will be the eternal fiery pit of hell.