Character Analysis
He's the dude who gets his father into piles of debt and sets off the events of the play. He's not, um, the most likeable dude.
He's Lazy and Mean
When we're first introduced to the characters, we see Strepsiades unable to sleep because he's fretting about all this debt, while Pheidippides sleeps soundly (and dreams of the horse racing that got them into this mess). When his dad tries to share his concerns, Pheidippides begs to be left alone to go back to sleep, just for five more minutes. Not exactly "Son of the Year" material, right?
He's Spoiled and Arrogant
When his father threatens to cut him off after he refuses to help the family get out of debt, Pheidippides retorts that he'll just run off to an uncle named Megacles, who is a big deal around those parts, apparently. According to him, "My godlike uncle Megacles won't leave me horseless. I'll go to him and pay you no mind" (124-125). Funny enough, we never meet Megacles, so he must not be too big of a presence in his nephew's life.
He's Smart—But He Doesn't Put the Noggin to Good Use
Pheidippides is smart enough to learn the Thinkery's lessons—so, he seems to be sharper than his dad. However, he puts them to even worse use than his dad could ever have imagined—he beats his dad, then justifies the violence by using his newfound logic. Only after that incident does Strepsiades become convinced that maybe the Thinkery's brand of instruction isn't all that awesomesauce.