Sly Sludge was first voiced by Martin Sheen. In later episodes, he is voiced by Jim Cummings. Sludge is usually found trying his way through some sort of get-rich-quick scheme. He likes to make a fast buck by promising to "take care" of trash or toxic waste. Of course, nothing is ever disposed of correctly.
Sly Sludge is short and rotund, with patchy, black or brown hair (it appears to vary). He is either going bald, or it is a side-effect from the toxic chemicals he constantly deals with. His remaining hair is long and past his shoulders. He has shaggy black eyebrows.
Sludge often wears yellow rubber gloves. His clothes are khaki, usually cover-alls or some sort of unofficial uniform, and he wears black boots.