- Born: 1521
- Died: 1590
- Sons: Mogami Yoshiakira, Mogami Yoshitoki, Mogami Yoshihisa, Mogami Yoshiyasu
- Distinction: Dewa warlord
Yoshimori was a son of Mogami Yoshiharu, who was a cousin of the lord of the Mogami, Yoshisada. When Mogami Yoshisada died without an heir in 1523, the 2-year old Yoshimori was chosen to succeed him. He ruled from Yamagata castle and clashed with the Uesugi, Date, and numerous local houses to expand the Mogami domain. He supported Date Tanemune in the Tenbun no ran and his daughter Yoshiko was married to Date Terumune, father of the famous Masamune. In 1571 Yoshimori indicated that he wished to name a young son as his heir, bypassing Mogami Yoshiakira. A faction of retainers loyal to Yoshiakira intervened to place Yoshimori in confinement and force the succession of Yoshiakira.
- Initial text from Sengoku Biographical Dictionary (Samurai-Archives.com) FWSeal & CEWest, 2005