J. Geil is the man responsible for the murder of Polnareff's sister, earning him Polnareff's desire for revenge.

J. Geil expend most of his time hiding from plain view, preferring to have a partner in which to rely on. This made him a perfect candidate for Hol Horse who like him believes working in pairs is best. He would hide in the shadows while Hol Horse broke the glass needed for his stand to work and sometimes they would do combination attacks, such as Hol Horse breaking glass and J. Gail attacking while Hol Horse shot a bullet from his Stand, the Emperor, locking the enemy in a mortal circle.

Like his mother he had a deformity that give him two right hands.

(Source: JJBA Wikia)