Red Boy (simplified Chinese: 红孩儿; traditional Chinese: 紅孩兒; pinyin: Hóng Hái-ér; Wade–Giles: Hung Hai-Erh; Vietnamese: Hồng Hài Nhi, Japanese: Kōgaiji) was a character featured in the novel Journey to the West. Red Boy was also known as the Boy Sage King (聖嬰大王), and had been the son of Princess Iron Fan and the Bull Demon King, a sworn brother of Sun Wukong from 500-years-earlier. Through the orders of his father, Red Boy was told to be the protector of the Fiery Mountains due to his supreme abilities when it came to fire, abilities he had cultivated for over 300 years.
Through this, Red Boy had developed True Samādhi Fire (三昧眞火, Pinyin: Sānmèi-zhēnhuǒ), which enables him to shoot fire inextinguishable by water and smoke from his eyes, nostrils and mouth. Samādhi is the Sanskrit word for concentration.
Sun Wukong had battled against Red Boy in hopes of returning his master Xuanzang. Red Boy did not believe Wukong's statement that Red Boy's father (the Bull Demon King) was his sworn brother, which technically made Wukong a relation of his.
Red Boy then tried to kill Wukong by controlling five carts (each one representing one of the Five Elements) that emitted in great amount of fire that had the power to blot out the heavens, but Wukong cast a fire resistance spell and chased after Red Boy, who had went back into his cave, thinking he had defeated Wukong.