The Poopsmith is just a regular guy with a very crappy job. Literally. It's unclear whether "The Poopsmith" is his actual name, as it's used occasionally with an integral article, but often without. His body is peach-colored and egg-shaped, and he has small blue legs and feet, a white head, and an enormous underbite. He wears a pair of large orange gloves stained with whatsit, and he is usually seen carrying a large shovel. The Poopsmith has taken a vow of silence and rarely officially speaks (except in email thunder, where he sings the opening song), nor does he seem to ever display any emotions or facial expressions. He does occasionally hold up signs to communicate, however. He is sometimes seen poking his shovel as a half-gesture, similar to how his Old-Timey incarnation, The Demon, uses his pitchfork.
While it is still unclear exactly what his job is, The Poopsmith has been employed by The King of Town, apparently to shovel whatsit for a living. In Homestar Ruiner, Strong Bad describes The Poopsmith's job as being the King's "personal bodyguard-slash-mime-slash-poosmith." He also works as a mail carrier, as seen in Compy Catalog. While he never seems to transfer whatsit between his constantly-soiled gloves and anything he touches, the inherently filthy nature of his job tends to keep him out of most social circles; for example, he is apparently banned for life from Strong Bad's Swimming Pool, as seen in keep cool. Despite this, he seems to be held in deep respect by the other characters. For example, Strong Bad has refrained from hurting The Poopsmith, figuring "the guy shovels crap for a living so his tolerance for pain's gotta be through the roof." He even made two cakes for The Poopsmith (though he threw one of them at Strong Sad). The Poopsmith also seems to be a good friend of Pom Pom.
During disconnected, The Poopsmith is depicted as being the King's law enforcement agent, defending the King and his "municipality" from the rock-throwing disobedience of Strong Body. He also has some musical talents: he plays the cymbals for the K.O.T.H.S. Junior Varsity Marching Band, which made its first appearance in Fall Float Parade; and is the lead vocalist for All the King's Men! despite never speaking (he simply gestures with the microphone).
In KOT's VOQPCS!, The Poopsmith is married to the pleasant odor of a bouquet of flowers, but they died after coming into contact with his stench.
In Halloween toons, the Easter eggs are often triggered by clicking on something in the same scene as The Poopsmith. They usually trigger a Homsar appearance.