The story
Quoting Clifford Edmund Bosworth, "the origin of the name Zangī is unclear; an obvious meaning would be 'black African' [from Persian زنگی (zangi)], possibly relating to a swarthy complexion, but this would be unusual for a Turk". Another theory considers the meaning "protector of cattle", compare 19th century Kirg. Zeñ-baba "protector spirit of cows".
Etymology from Wiktionary, CC BY-SA 4.0.