Sakonji Urokodaki

Giyu Tomioka: A former student and the current Water Hashira.
Sabito: Urokodaki's most promising student, who died during the Final Selection. He later appeared as a spirit to help Tanjiro.
Makomo: A former apprentice who also died during the Final Selection, similarly to Sabito. She appeared to Tanjiro as a spirit to assist him.
Tanjiro Kamado: The final student, who was guided by the spirits of Sabito and Makomo. He was the one who eventually defeated the Hand Demon that had killed many of Urokodaki's past students.

KimetsuNoYaiba
Sakonji Urokodaki's students include Giyu Tomioka, Sabito, Makomo, and Tanjiro Kamado. While Tomioka and Tanjiro survived and became Demon Slayers, Sabito and Makomo tragically died during the Final Selection, killed by the Hand Demon. Both Sabito and Makomo, along with Tomioka, were instrumental in helping Tanjiro during his training, appearing to him as spirits to guide

He is depicted as being around 66 years old

Sakonji Urokodaki wears a mask to hide his gentle and kind face because demons used to mock him for it. The mask conceals his emotions, preventing demons from judging or taking advantage of his soft features.
Masks hide his emotions: The tengu mask serves to conceal Urokodaki's face and his emotions, which makes him appear more intimidating to demons.
Demons used to mock him: The reason he started wearing the mask was because demons found his actual face too gentle and kind.
His face is described as gentle: According to a "Taisho Secret" in the series, Urokodaki has a very gentle and calm face that demons found amusing.

Sakonji Urokodaki is a retired former Water Hashira from the Demon Slayer Corps and the master of Tanjiro Kamado, Giyu Tomioka, Sabito, and Makomo. He is a powerful and skilled cultivator of the Water Breathing style, known for his stealth, speed, and keen sense of smell. After his students Sabito and Makomo died, he became a recluse but eventually took on Tanjiro as his student.
Role in the story
Teacher: He trained Tanjiro in the Water Breathing style, a crucial part of Tanjiro's journey to become a demon slayer.
Mentor: He also trained Giyu Tomioka, Sabito, and Makomo before they died.
Protector: He sent a letter to the leader of the Demon Slayer Corps, Kagaya Ubuyashiki, to request forgiveness for Tanjiro harboring a demon, and pledged that he, Tanjiro, and Giyu would commit seppuku if Nezuko ever killed a human.
Abilities and skills
Water Breathing: He is a master of the Water Breathing style, having cultivated it himself.
Stealth and speed: He possesses incredible speed and can move without making a sound.
Keen sense of smell: Like Tanjiro, he has a very acute sense of smell, which he uses to track demons.
Physical strength: Even in his old age, he is physically strong enough to keep up with a young and fit Tanjiro.
Personality
Stern but caring: He is a stern and demanding teacher, but he cares deeply for his students.
Guilt-ridden: He feels guilt over the deaths of his students