Cleon (ca. 475-422 B.C.) was an important historical figure in classical Athens. He served as an Athenian general during the Peloponnesian Wars and was distinguished by a strongly populist bent, including advocacy for the urban middle classes and newly rich (merchants and artisans) in opposition to the hereditary aristocracy and rural residents. Most of our historical knowledge of him, unfortunately, is from works by Thucydides and Aristophanes who strongly disliked him. Aristophanes, in particular, associates (probably accurately) the anti-aristocratic party of Cleon with hatred of Sparta (which was an aristocratic society); Cleon in particular is associated with warmongering and extremism, such as advocacy of killing all the men and enslaving all the women and children of Mytilene, a small state allied to Athens that wished to remain neutral in the war.
The Wasps is a direct attack on an aspect of Cleon's political activities. The courts, with their citizen juries, were often associated with the democratic "rabble" in Athens. Cleon's associates were particularly notorious in using lawsuits or threats of lawsuits, often on vague or weak charges, to take down their political opponents. The character of Philocleon (lover of Cleon), combining a love of the courts and complete lack of social graces, is intended as a direct critique of the followers of Cleon, whom Aristophanes is portraying as in love with lawsuits for their own sake, and lacking human kindness and generosity, as well as only manipulating the "demos" (non-aristocrats) to advance their own agenda rather genuinely caring about the poor, as we can see in this speech by Philocleon about the power he wields as a jurist:
From the moment I leave my bed, men of power, the most illustrious in the city, await me at the bar of the tribunal; the moment I am seen from the greatest distance, they come forward to offer me a gentle hand -- that has pilfered the public funds