was a noble surname bestowed by the Emperors of Japan upon members of the imperial family who were excluded from the line of succession and demoted into the ranks of the nobility since 814. The Minamoto was the most powerful and most important clan of all four great clans that dominated Japanese politics during the Heian, Kamakura, Muromachi and Edo periods in Japanese history—the other three were the Fujiwara, the Taira, and the Tachibana.
The Minamoto clan is also called the Genji, or less frequently, the Genke, using the On'yomi readings of gen for "Minamoto", while shi or ji means "clan", and ke is used as a suffix for "extended family".
The practice was most prevalent during the Heian period (794–1185 AD), although its last occurrence was during the Sengoku period. The Taira were another such offshoot of the imperial dynasty, making both clans distant relatives.
In May 814, the first emperor to grant the surname "Minamoto" was Emperor Saga, to his seventh son—Minamoto no Makoto, in Heian-Kyō (modern Kyōto).The most prominent of the several Minamoto families, the Seiwa Genji, descended from Minamoto no Tsunemoto (897–961), a grandson of Emperor Seiwa. Tsunemoto went to the provinces and became the founder of a major warrior dynasty. Minamoto no Mitsunaka (912–997) formed an alliance with the Fujiwara. Thereafter the Fujiwara frequently called upon the Minamoto to restore order in the capital, Heian-Kyō (modern Kyōto).Mitsunaka's eldest son, Minamoto no Yorimitsu (948–1021), became the protégé of Fujiwara no Michinaga; another son, Minamoto no Yorinobu (968–1048) suppressed the rebellion of Taira no Tadatsune in 1032. Yorinobu's son, Minamoto no Yoriyoshi (988–1075), and grandson, Minamoto no Yoshiie (1039–1106), pacified most of northeastern Japan between 1051 and 1087.
The Seiwa Genji's fortunes declined in the Hōgen Rebellion (1156), when the Taira executed most of the line, including Minamoto no Tameyoshi. During the Heiji Disturbance (1160), the head of the Seiwa Genji, Minamoto no Yoshitomo, died in battle.