Yamagata Masakage (山県 昌景, 1524 – June 29, 1575) was a Japanese samurai warrior of the Sengoku period. He is known as one of the "Twenty-Four Generals of Takeda Shingen". He was famous for his red armour and skill in battlefield, and was a personal friend of Takeda Shingen. He was the younger brother of Obu Toramasa who was also a retainer of Shingen leading the famous "red fire unit" (derived from Shingen's slogan Fūrinkazan). After his brother committed Seppuku as a cover for Takeda Yoshinobu's failed rebellion, Masakage took the red fire unit title and outfitted his cavalry in bright red armor. It was said that his cavalry would always charge first in battle; sowing confusion and panic in the enemy ranks.
Yamagata was a fierce warrior who fought in many battles and was given a fief in Shinano. He was present at the Battle of Mimasetoge in 1569 and captured Yoshida Castle, a Tokugawa possession, during the Mikatagahara Campaign (1572–73).
He was present for the following Battle of Mikatagahara. His last campaign was in the ill-fated Battle of Nagashino in 1575, in which he tried to persuade Katsuyori to honorably withdraw.
Ii Naomasa from the Tokugawa clan was inspired by Yamagata's red colour; he made tribute to him by naming his army the "Red Devil Brigade."
According to legend, Shingen called out to Yamagata from his deathbed in 1573 and ordered him to plant his banners at the Seta Bridge, the traditional eastern gateway to Kyôto.
Yamagata is one of the main characters in Akira Kurosawa's epic film Kagemusha.