Yes, the Bible tells about some very evil people - and one reason they're included is to warn us about the dangers of following their example. The Bible says, "These things happened to them as examples and were written down as warnings for us" (1 Corinthians 10:11).
It's hard for me to select one individual as the absolute worst person in the Bible; the Bible's list of evil people is long! Certainly, however, Judas would be near the top of anyone's list. No one had a greater opportunity to believe in Jesus and follow Him; as one of his 12 disciples, Judas watched every miracle Jesus did and heard every word He taught. And yet he betrayed Jesus for money - an act of treachery that led to Jesus' death. Later, Judas killed himself - but his evil deed couldn't be reversed (see Matthew 27:5).
When I think of evil people in the Bible, however, I often think of King Manasseh in the Old Testament. (You can read about him in 2 Chronicles 33.) He banned the worship of God and forced the people instead to follow pagan practices - even sacrificing his son to pagan gods. To make matters worse, he ruled the Jewish nation longer than any other king.
But the story of Manasseh doesn't end there. In time, Manasseh repented - and God forgave him, and Manasseh spent the rest of his life undoing the evil he had done. If God could forgive Manasseh, can't He forgive you?