The Mōri Clan (毛利氏 Mōri-shi) was a family of daimyō, descended from Ōe no Hiromoto and settled in Aki province. Their name is derived from a shōen in Mōri, Aikō district, Sagami province. Hiromoto's generation began to call itself Mōri.
After the Jōkyū War, Mōri was appointed by the jitō office of a shōen in Aki. During the Kamakura Period, Mōri was one of the prominent Gokenin families due to the fame of his ancestor Hiromoto.
By the end of the Kamakura shogunate, Mōri was distant from the shogunate and showed a favorable attitude toward Ashikaga Takauji.
In the Sengoku Period, Mōri Motonari was successful in expanding his power throughout Aki Province and then into other neighboring provinces. In his generation, Mōri became daimyo of a local Gokenin.
After a feud with Toyotomi Hideyoshi, who led his troop as Oda Nobunaga's general, the two sides made peace and Mōri remained as daimyo, maintaining five provinces in Chūgoku.
In 1600, Mōri Terumoto led the Western Army in the Battle of Sekigahara nominally. The Western Army lost the battle and the Mōri clan lost three provinces to the east and moved its capital from Hiroshima to present-day Hagi, Yamaguchi.
The new fiefdom, Mōri han consisted of two provinces: Nagato and Suō. Derived from the previous ones, Mōri han was commonly referred to as Chōshū han.
After the Meiji Restoration, the han and daimyo system was abolished. The Mōri were titled as dukes.