The introduction to the book of Proverbs in the ESV Study Bible notes that the characters in the book usually serve as idealized portraits.

In other words:

They denote people exemplary for their virtue and wisdom or especially despicable for their evil. The literary name for this is “caricature”: portraits of people with features exaggerated for easy identification.

The positive figures serve as ideals for the faithful, to guide their conduct and character formation.

The negative figures are exaggerated portraits of those who do not embrace the covenant, so the faithful can recognize these traits in themselves and flee them.

“To read Proverbs well,” the introduction notes, “one must have a good grasp of who the character types are and what function they serve in the book.”

It then identifies the three most obvious characters in the book:  the wise, the fool, and the simple.

[1. The Wise]

Proverbs urges its readers to be wise, that is, to embrace God’s covenant and to learn the skill of living out the covenant in everyday situations (cf. Prov. 2:2).

The wise person has done that (cf. Prov. 10:1); usually Proverbs focuses on the one who has made good progress in that skill, whose example is worth following (cf. Prov. 9:8b).

[2. The Fool]

The fool is the person steadily opposed to God’s covenant (cf. Prov. 1:7b).

The setting of Proverbs assumes there can be fools even among God’s people.

There are three Hebrew terms translated “fool” (kesil’ewilnabal), with little difference among them.

This kind of person resists even the offer of forgiveness found in the covenant (Prov. 14:9; 15:8).

These people are dangerous in their influence (Prov. 13:20; 17:12) and cause grief to their parents (Prov. 10:1); but they are not beyond hope (Prov. 8:5).

[3. The Simple]

The simple is the person who is not firmly committed, either to wisdom or to folly; he is easily misled (cf. Prov. 14:15).

His trouble is that he does not apply himself to the discipline needed to gain and grow in wisdom.

The introduction goes on to provide three additional categories for the characters.

[4. Co-Referential Characters from Different Positive Angles]

Proverbs also uses other terms, both positive (e.g., righteous, upright, diligent, understanding, prudent) and negative (e.g., wicked, lazy, lacking sense).

These do not designate different groups of people from the wise and the fools; rather, the terms are commonly “co-referential,” i.e., they apply to the same people looked at from different angles.

The righteous is the one who has embraced the covenant, seen from the perspective of his faithfulness to God’s will;

the wise is the same person, seen from the perspective of his skill in living out God’s will;

the prudent is the same individual seen as one who carefully plans out his obedience.

[5. Co-Referential Characters Different Negative Angles]

Likewise, the wicked is the one who rejects God’s covenant, seen from the angle of his opposition to God;

the fool is this same person, seen from the angle of the stupid course of life he has chosen.

The co-referential use of these terms helps the reader to discern the many-sided fruits of godliness and ungodliness.

[6. Gradations of Negative Characters]

Beyond the co-referential negative terms, there are some gradations.

The scoffer is worse than a fool (21:24).

The person wise in his own eyes is almost beyond hope (cf. 26:12). The difference is one of hardness in unteachability (the great sin in Proverbs).

The simple is not as far gone as the fool.

All of these are what the OT calls “uncircumcised” in heart, and what Christian theology calls “unregenerate.”