Minamoto no Sanetomo
Hōjō Tokimasa, who was the father-in-law of the first "shōgun" Minamoto no Yoritomo, father of Hōjō Masako, became the first "shikken" in 1203, after Yoritomo's death. The "shikken" was the chief of the "mandokoro" at that time. Tokimasa became the de facto ruler of the shogunate by monopolizing decisions for the young "shōguns" Minamoto no Yoriie and Minamoto no Sanetomo (Yoritomo's sons and Tokimasa's own grandsons), executing whoever got in his way, family or not. Tokimasa's own grandson (Yoriie) and great-grandson were murdered on Tokimasa's orders, a year after he replaced Yoriie (the second "shōgun") with Sanetomo.