Eidu (Chinese: 額亦都, 1562-1622) was a Manchu officer and a member of the Niohuru clan.
Eidu's grandfather had established a home in a valley of the Yengge ("wild grape") mountain range, which formed the easternmost spur of the Changbai Mountains, in the southeast area of the present day Jilin.
Eidu's parents were murdered in a feud when he was very young, and he escaped only through the protection of a neighbour. At the age of twelve, he took revenge by killing his parents' murderer, after which he fled to the home of an aunt, who was married to the chieftain of the fortress of Giyamuhu. Here he became a close friend of the chieftain's son, Gahasan Hashu, who later married Nurhaci's sister.
In 1580, Nurhaci, then twenty-one years old, passed through Giyamuhu and stopped at the chieftain's home. The eighteen-year-old Eidu was so impressed by his qualities of leadership that he attached himself to Nurhaci and remained his close associate for more than forty years.
In 1583, he accompanied Nurhaci and proved himself an able fighter. Four years later he captured the town of Barda, and received from Nurhaci the title of baturu, "conquering hero." After a long and successful career of military achievement, he joined the Bordered Yellow Banner in 1615, and was appointed as one of the five principal dignitaries in government the following year. In 1617 he captured a number of Ming fortresses in company with Anfiyanggu, and in 1619, was at the forefront of the decisive battles waged by Nurhaci against the three armies of Yang Hao. As reward for his services, he was given a sister of Nurhaci as one of his wives.
Eidu's second son, Daki, was brought up in the royal establishment, and married the fifth daughter of Nurhaci. When Daki spoke out against Nurhaci's sons, Eidu put him to death, prompting Nurhaci to call Eidu his most patriotic officer.
Eidu died in 1621. In 1634, he was posthumously awarded the rank of a viscount, which was inherited by his sixteenth son, Ebilun. In 1636, his rank was raised to that of duke (non-hereditary). His name was entered in the Imperial Ancestral Temple, his tomb was moved to a location near that of Nurhaci. A stone tablet was erected in front of the tomb in 1654. The rank of viscount was taken from Ebilun in 1637, due to a misdemeanor, but was restored in 1713 and given to his son, Yende. After Yende was made a duke in 1724, the title of viscount was inherited by other branches of Eidu's family.