Gedds are blue monkey-like creatures native to the Yeerk homeworld and were the first species the Yeerks infested. Gedds are an odd race, they have yellow eyes, three-fingered hands, and webbed toes, they're not terribly bright, they have poor vision, poor motor skills, and although they have two legs, with one leg being longer than the other, they are unable of balancing them, they keep one or both hands on the ground for balance. Their mouths are hard to control, and any Gedd-Controller will have problems speaking effectively.
Because they are slow and inefficient, the Gedds formed a symbiotic relationship with the Yeerks, who helped them survive in exchange for being hosts. However, after the unfortunate incident of Seerow's Kindness interfered, the Yeerks became greedy and the Gedds became just one of their enslaved races. They are used throughout the series not as shocktroops, but as host-bodies for young/low-ranking Yeerks, but aren't seen much.