En no Gyōja

was the former leader of the Tsuchigumo clan and the grandfather of Hotaru.

Background
During the Third Great Shinobi World War, he made a peace treaty with Hiruzen Sarutobi. He developed a jutsu capable of destroying an entire village which the Third Hokage proclaims it a kinjutsu because of its power.

Influence
The name of this character comes from the Japanese ascetic and mystic, the legendary founder of the Japanese religion. The real-life En no Gyōja was born in 634 and is venerated as a mountain saint and a bodhisattva. Many supernatural powers are attributed to him.

In the horror novel Ring by Japanese author Kōji Suzuki, a statue of En no Gyōja gives supernatural powers, including precognition, to the mother of antagonist Sadako Yamamura. Sadako herself is born with the same powers, implying that En no Gyōja is her father. The famous horror film Ring is based on this novel.

Trivia

 * means ascetic. is a surname. when pronounced as eki, it means war campaign or battle; when pronounced as yaku, it means service, role, or use.