Sergeant Keroro commands the Keroro Platoon, formally designated as the Gamma Planetary System's 58th Planet Space Invasion Army Special Tactics Platoon. This official military title signifies his leadership role. He appears as an adult Keronian with green and white skin, wearing yellow headgear adorned with a red star and a matching star insignia on his belly. He stands precisely 55.5 centimeters tall and weighs 5.555 kilograms. A recurring visual gag depicts him with a large, comical black afro after explosions, referencing the anime's first ending sequence.

Keroro's personality mixes laziness, distractibility, and selfishness with underlying empathy and leadership potential. He frequently neglects invasion duties to build Gundam models, watch anime, or scheme for money. Earth's lower humidity weakens Keronians, significantly reducing his physical capabilities and motivation. However, high humidity exposure triggers "Keroro From Back Then," reverting him to a ruthless, hyper-competent state with enhanced strength, speed, and energy beam attacks. Prolonged exposure risks madness, requiring intervention like absorption by a Nyororo. Despite his flaws, he shows unexpected kindness, refusing to abandon those in need and acting as a capable caretaker for entities like Kiruru. He also demonstrates strategic brilliance and combat prowess when motivated, potentially exceeding elite Keron Army members.

His childhood on Keron involved troublemaking and bullying, particularly toward Dororo. Inspired by his father, a renowned war veteran, he pursued a military career. Early arrogance often led to failure, though he showed resilience. He shares a longstanding connection with platoon members Giroro, Pururu, and Zeroro. Keronian aging differs from Earth; he is approximately 10,500 Keronian years old, with birth likely around 1970 in the Keronian calendar.

Relationships profoundly shape his actions. He harbors deep fear and admiration for his strict father. Among humans, he forms a close bond with Fuyuki Hinata, whose appeals to friendship often halt invasion plans. He views Fuyuki's mother, Aki, as a maternal figure. Conversely, he cowers before Natsumi Hinata due to her harsh punishments, though their dynamic evolves toward sibling-like rapport. Within his platoon, his leadership unites the disparate members despite their frequent frustrations. He retains complex ties with Giroro and Dororo rooted in their shared past.

Keroro uses formal military speech patterns: "waga hai" (我が輩) for himself, "dono" (殿) for others, and ends sentences with "de arimasu" (であります). He employs varied styles for comedic effect, including a signature scheming laugh ("Ge~ro gero gero..."). His strengths include unexpected skills like advanced cleaning and curling honed through household chores, ninjutsu proficiency learned from Dororo, and engineering aptitude. He can channel the Keron Star to issue commanding "Super ☆ Captain's Orders" and subdue threats. Weaknesses encompass cowardice, poor impulse control, and fears of his father, broken Gundam models, invasion deadlines, Nyororos, and "Butt Firecrackers".

Character development shows gradual maturation. While often blamed for the platoon's failures, he takes responsibility in critical moments, protecting allies or Earth from external threats. Instances like defying Keron Army orders to safeguard Kiruru or mediating platoon conflicts reveal his capacity for growth and hidden leadership depth.