Gorilla, whose real name is Kreis, is a supporting character from the manga who serves as the primary motivation for the priest Sein to embark on his journey. He is a human warrior and a childhood friend of Sein, hailing from the same village. As a young man, he shared a dream with Sein of becoming an adventurer and leaving their mark on the world.

Gorilla is a physically imposing individual, characterized by his muscular build, slicked-back and spiky dark-brown hair, and brown eyes. He dresses practically for travel and combat, wearing a light-colored tunic with a belt, a short brown coat, and baggy black pants. He also sports bandage wraps around his ankles and forearms, and carries a sword strapped across his back.

His personality is defined by a strong-willed, proactive, and ambitious nature. This is most clearly demonstrated by his decision to adopt the moniker "Warrior Gorilla." His real name is so obscure that even his best friend, Sein, forgets it, and he insists everyone call him by this chosen name. The origin of this name lies in his central motivation: a deep-seated fear of being forgotten. As a young man, he stood before the weathered statue of a forgotten hero and declared to Heiter and Sein that he would not suffer the same fate. He reasoned that to be an unforgettable hero like Himmel, one must first have an unforgettable name, leading him to christen himself "Warrior Gorilla". This act defines his character; his entire journey is driven by the desire for immortality through legacy.

In the story, Gorilla functions as the unseen goal for Sein. He left their shared village on an adventure a decade before the main events of the series, promising to return in three years. When he fails to do so, Sein spends years believing he might be dead. However, upon joining Frieren's party, Sein dedicates his travels to finding his lost friend. The party follows the trail of "Warrior Gorilla," discovering that he has been traveling from town to town, leaving a strong impression on the locals by exterminating monsters and speaking fondly of his friend Sein. This pursuit ultimately leads Frieren's party to a town where they learn Gorilla has headed towards the trading city of Tür, a path that forces Sein to leave the group to follow the lead alone.

His most significant relationship is with Sein, who he constantly tried to persuade to leave their village and join him on adventures. Sein’s guilt over refusing this offer and his determination to find Gorilla is a core component of his character arc. Gorilla also shares a connection to the hero Heiter, who witnessed his youthful vow and humorously nicknamed Sein "Priest Goatee" to mirror Gorilla's own naming philosophy. Physically, his appearance is noted to somewhat resemble the ancient elf Kraft.

While he is a capable warrior skilled enough to have survived a decade of adventuring in a dangerous world, his specific combat abilities are not detailed in the early parts of the story. As a character, Gorilla develops from an unnamed village boy with a dream into a figure of local legend, his unique name ensuring that travelers and townsfolk remember him years later. His story is one of pursuing glory not just through deeds, but through the deliberate crafting of one's own identity. Later developments reveal that his real name is Kreis and that he is a member of the Shadow Warriors, a group of assassins serving the Empire, where he later works undercover as a blacksmith while caring for his younger sister.