Peggy Matsuyama, known as Momorenger, is a core member of the Himitsu Sentai Gorenger team. She is an eighteen-year-old woman of Eurasian heritage, with a Swiss father and a Japanese mother. Before becoming a ranger, Peggy was assigned to the Hokkaido branch of EAGLE, where she worked as a chemical analyst and a special weapons engineer specializing in explosives. Her entire base was wiped out in an attack by the Black Cross Army, leaving her as the sole survivor. This event directly leads to her recruitment into the Gorenger team.

In terms of personality, Peggy is portrayed as a fashionable young woman, often seen in the fashion of the era wearing go-go boots and hot pants. Beyond her stylish exterior, she possesses a dignified, kind, and serious demeanor when the situation demands it. She is lethal and efficient in combat against her enemies. Within the team dynamic, she acts as a calming and controlling presence, often reining in the more hot-headed or clumsy members like Kenji Asuka and Daita Oiwa, filling an older sister-like role.

Peggy's primary motivation is to combat the Black Cross Army that destroyed her former life. Her specific role in the story is that of the team's demolitions expert and spy. Her technical expertise is vital to the team's operations, as she is responsible for developing and maintaining their explosive-based weaponry. A key example of her importance is that without her, the team cannot perform its ultimate finishing move, the Gorenger Storm. She is also a master of disguise, frequently undertaking undercover espionage missions, especially those involving other women.

Peggy shares deep bonds with her fellow Gorengers, particularly acting as a supportive figure for the younger members of the team. Her development throughout the series is highlighted in episodes where she faces personal crises. In one instance, she is subjected to a hypnotic block that renders her unable to transform into Momorenger. This storyline emphasizes her psychological strength and her need for the unconditional support of her teammates to overcome mental and emotional limitations, ultimately recovering her confidence and ability to fight. She also has a past romantic connection with a superior officer at her former base who was killed in action, a loss that a monster once exploited against her.

As Momorenger, Peggy possesses several notable abilities and pieces of equipment. She is a skilled fighter, proficient in high kicks and judo. Her signature weapons are her heart-shaped earrings, which double as high-impact bombs that she throws at enemies while saying a taunt. She also uses heart-shaped Momo Card throwing shurikens and the Momo Mirror, a device used to jam and confuse opponents. For reconnaissance, she has the Momo Ceceli tracking device. For the team's final attack, she helps handle the Ranger Ball, a powerful projectile passed among the team like a soccer ball before it is kicked at the enemy to destroy it. In terms of transportation, she rides in the sidecar of the Green Machine.