Keroro is the son of one of the greatest military officers of the planet Keron, located in the Gamma Storm Cloud System and was naturally compelled to enlist in military service to the Keron Forces. Somehow despite his laziness and general incompetance, he managed to rise to the position of Sergeant and was given command of an elite platoon of Keron soldiers and an important assignment to act as the primary scouting force on the planet Earth.
Despite his attempts to remain hidden, he was discovered by the youngest members of the Hinata household, Natsumi and Fuyuki Hinata and was immediately captured. Shortly afterward the Keron Armada believing that the secrecy of their invasion was compromised, immediately fled and abandoned the Keroro Platoon on Earth.
With nowhere to go, marooned on an alien planet, and separated from the other members of the Keroro Platoon; Natsumi decided that Kero would not be a Prisoner of War (a.k.a Freeloader) and instead was pressed into servitude as the housekeeper of the Hinata household. It was a role that Kero originally seemed to despise but he seems to have adjusted remarkably well; in fact "too well" as some might argue. Ever since he convinced Aki Hinata that he deserves to be paid minimum wage for his work; he has been busy blowing his allowance on his obsessive hobby of Gundam models than trying to conquer the planet.
Although the Keroro Platoon has since been reunited and the majority of them actively seek to complete the invasion, their elaborate schemes have always failed miserably each and every single time. Even though many believe that the single greatest obstacle to the Keroro Platoon's success is the Hinata family; a few realize that Kero himself is probably their biggest hindrance.