Minamoto no Kugyo
Kugyô was the eldest of three children who Minamoto no Yoriie had with a wife from the Kamo family; his younger brothers were known as Senjûmaru and Zengyô. He also had two half-siblings, Minamoto Ichiman and Take no gozen, born to Wakasa no Tsubone, Yoriie's wife from the Hiki clan.
Kugyô survived the Hôjô clan extermination of the Hiki clan, and was then adopted by his uncle Minamoto no Sanetomo at the suggestion (or urging) of Sanetomo's mother, Hôjô Masako. Kugyô was then entered into training at the Buddhist temple of Onjôji (aka Miidera, near Kyoto) and the Shinto shrine of Tsurugaoka Hachimangû in Kamakura.
Kugyô is said to have hidden behind a large ginkgo tree just to the side of the main stairs within the shrine, jumping out to strike Sanetomo. Some sources make no mention of the tree, however, indicating that he emerged from beneath or to the side of the stairs. While some accounts make no mention of Sanetomo's guards or retinue otherwise, even those which do indicate the presence of guards or an entourage make no mention of how the assassin was able to attack and kill the shogun so quickly and easily without having to go through those others.