Carl Carlson was
Homer Simpson's supervisor (or so was stated in one episode) at the
Springfield Nuclear Power Plant before Homer's promotion to
Safety Inspector. He's Lenny's best friend, and the two are nearly always seen together. He holds a degree of some sort in
nuclear physics. He also owns a nice red
convertible, although we've never seen how he lives (Lenny lives in a
hovel eating
dog food).
Carl infamously made Homer, Barney and Lenny break down into tears in Moe's Tavern one evening by highlighting their flaws, and turned to the camera and said, "See, this is why I don't talk much".
In terms of rendering, Carl is very old school by Simpsons standards - very distorted, almost a caricature when compared to later characters.