Usually a description, not a person
Most Old Testament uses of Belial do not introduce a figure with a story or family line. The Hebrew term behind it, beliyya'al, is commonly understood to carry the sense of worthlessness or destructive wickedness. In the KJV, it often appears in descriptions of people who have set themselves against God and his ways.
For instance, Hophni and Phinehas were priests at Shiloh, yet they dishonoured their office and treated the Lord's offerings with contempt. Their behaviour, not their ancestry, is why Scripture applies this severe label to them (1 Samuel 2:12).
Now the sons of Eli were sons of Belial; they knew not the Lord.
Wicked people and wicked acts
Belial language appears when Scripture warns about rebellion that spreads harm. Moses speaks of corrupt people who might lead an Israelite town into idolatry (Deuteronomy 13:13). The word marks a serious turning away from the Lord, not a minor mistake.
Judges uses the term for the men of Gibeah who surrounded a house and demanded that the male visitor be brought outside to them (Judges 19:22). Later, after the visitor's concubine was sent out, those men abused her through the night, and she died (Judges 19:25). It is a painful account, but it shows why the Bible treats such rebellion as destructive to real people.
But the men would not hearken to him: so the man took his concubine, and brought her forth unto them; and they knew her, and abused her all the night until the morning: and when the day began to spring, they let her go.
Paul's use of the name
The New Testament uses Belial once. Writing to the Corinthian church, Paul contrasts Christ with Belial as opposites (2 Corinthians 6:15). Here the word sounds like a personal name, not simply a label for immoral people.
Paul does not give Belial a biography or explain exactly how his readers understood the name. Many Christians take it as another name for Satan, or for the spiritual power of evil that resists Christ. Others stress the broad contrast Paul is making between Jesus and everything opposed to God. Either way, the point is not curiosity about dark powers. It is loyalty to Christ.
And what concord hath Christ with Belial? or what part hath he that believeth with an infidel?
What can be said with confidence
Belial is not presented like David, Moses, or Paul, with a detailed life story in Scripture. In the Old Testament, the term mainly identifies people and actions characterised by grave wickedness. In Paul's letter, it functions as the opposing side in his contrast with Christ.
Later Jewish and Christian writings gave Belial a larger role as a ruler of evil or a demon. Those writings may explain why Paul's audience recognised the name, but the Bible itself gives limited detail. So it is wise to stay close to the passages and let their central message stand: evil is real, but Christ calls his people to what is holy, true, and life-giving.