The Plentifuls are a race of small pudgy humanoids only a bit larger than Smurfs who reside in the Land Of Plenty. They are ruled by their king The Great Plentiful who is the keeper of the Horn Of Plenty which is the source of all their plentiful food which likely attributes to their rotund body shape. Because of their simple life with easy to acquire food, Plentifuls are very out of shape and even running short distances easily tires them out.
In the episode "The Horn of Plenty", the Plentifuls are sought out by the Smurfs in hopes of asking their king to lend them his Horn Of Plenty. At first the king refuses but his horn is quickly stolen by Gargamel. After the Smurfs reclaim the horn and use it to restore food to the forest, they return the horn to the Plentifuls who realize it is better to share food than to hoard it.