Also known as: Hatakeyama Yoshiharu (畠山義春), Uesugi Masashige (上杉政繁)

Son of Hatakeyama Yoshitsugu, he was one of Uesugi Kenshin's adopted sons. His legal wife was the daughter of Nagao Masakage.

In the beginning he was taken by Kenshin as a hostage, but his abilities were noticed by Kenshin, who adopted him. He became the head of the Joujou-Uesugi Clan and married one of Uesugi Kagekatsu's sisters. He was distantly related to the Uesugi Clan and was content with his standing within the clan. He distinguished himself in the numerous battles Uesugi fought against Oda Nobunaga and Houjou Ujimasa.

He fought for Kagekatsu in the Otate no Ran after Kenshin's death. Afterwards, he fought and checked invasion by the Oda army several times and was made master of Kaidu Castle. In 1584, his son (Kagekatsu's nephew) was sent to Toyotomi Hideyoshi (Kagekatsu had no sons of his own at the time). In compensation, he was exempted from military service.

In 1586, he accompanied Kagekatsu to the capital, but afterwards he left the Uesugi Clan, leaving his wife and children behind. In rage, Kagekatsu confined Masashige's wife (his sister) and children for almost ten years. There are various theories regarding the reasons for Masashige's defection, including slander from Naoe Kanetsugu, Kagekatsu's trusted commander and advisor, a close relationship with Shibata Shigeie, and mistrust from Kagekatsu because Masashige was also one of Kenshin's adopted sons.

He later became a vassal of Tokugawa Ieyasu and changed his family name back to Hatakeyama. He fought for Ieyasu in the Battle of Sekigahara in 1600 and lived in Edo until his death.