The actor who played Lex Luthor was only on the show for 7 years (he got tired of shaving his head), so for the past few years the writers had to get creative because Lex is Superman's most well-known villain. Now in the final season they are incorporating another Big League villain, Darkseid, the Lord of Apokolips. They are giving it an interesting twist, though. At this point Darkseid draws on the darkness within people & uses them for his evil bidding.
The truth is, all people do have a darkness within--the sin nature. Temptation does not come externally but internally, as we read in James 1:13-15. We all sin because we are sinners. Jesus Christ died to take the punishment for our sin, and He rose from the dead & is alive now to enable those who have trusted Him as Savior to overcome temptation.
Like Darkseid on Smallville, Satan can use the sinful desires within you against you if you let him, but the sin is already in you. If you accept Jesus' sacrifice for your sins you will be forgiven, & once you are forgiven the Holy Spirit will live in you to convict you of sin & enable you to live godly!