Yoritomo, who had become the first shogun of the bakufu, became Yasutoki's godfather 'eboshi-oya' and Yasutoki was given "yori" from Yoritomo's name and thus called Yoritoki.
幕府の初代将軍となった頼朝が烏帽子親となり、頼朝の頼を賜って、頼時と名乗る。