Shaka kaSenzangakhona (c. 1787–24 September 1828), also known as Shaka (the) Zulu (Zulu pronunciation: [ˈʃaːɠa]) and Sigidi kaSenzangakhona, was the king of the Zulu Kingdom from 1816 to 1828. One of the most influential monarchs of the Zulu, he ordered wide-reaching reforms that reorganized the military into a formidable force.

King Shaka was born in the lunar month of uNtulikazi (July) in 1787, in Mthonjaneni, KwaZulu-Natal Province, South Africa. The son of the Zulu King Senzangakhona kaJama, he was spurned as an illegitimate son. Shaka spent part of his childhood in his mother's settlements, where he was initiated into an ibutho lempi (fighting unit/regiment), serving as a warrior under Inkosi Dingiswayo.

King Shaka refined the ibutho military system with the Mthethwa Paramountcy's support over the next several years. He forged alliances with his smaller neighbours to counter Ndwandwe raids from the north. The initial Zulu maneuvers were primarily defensive, as King Shaka preferred to apply pressure diplomatically, with an occasional strategic assassination. His reforms of local society built on existing structures. Although he preferred social and propagandistic political methods, he also engaged in several battles.

King Shaka's reign coincided with the start of the Mfecane/Difaqane ("upheaval" or "crushing"), a period of devastating warfare and chaos in southern Africa between 1815 and 1840 that depopulated the region. His role in the Mfecane/Difaqane is controversial. He was assassinated by his half-brothers, King Dingane and Prince Mhlangana and Mbopha kaSithayi.

Shaka (roughly translated as "intestinal beetle") was born to the reigning Zulu king. He was the eldest of many sons, but was considered to be a bastard child and was sent away to live with his mother's tribe, known as the Elangeni, leaving his half-brother to rule the Zulu kingdom. At the time, the Zulu were a regional tribe relying on pastoral livestock, sorghum, and milk. When Shaka reached a suitable age, he and his mother were sent to the Mthethwa clan, the most powerful regional tribe. There, he matured, and served as a warrior under Jobe, and then for Dingiswayo, a respected warrior and chief of the clan. When Inkosi Dingiswayo discovered Shaka was royalty, he put him in charge of a regiment, helping to develop Shaka's military tactics and strategy.

After Inkosi Zwide, the king of the Ndwandwe (Nxumalo) nation, murdered Dingiswayo, Shaka sought to avenge his death. During that encounter, Zwide's mother, Ntombazi, a sangoma, was killed by Shaka. Shaka chose a particularly gruesome revenge on her by locking her in a house with jackals or hyenas inside. They devoured her, and in the morning, Shaka burned the house to the ground. Shaka continued his pursuit of Zwide. It was not until around 1825 that the two military leaders met in the vicinity of Pongola, near the present-day border of Mpumalanga, a province of South Africa. Shaka was victorious in battle, although his forces sustained heavy casualties, including his military commander, Mgobhozi Ovela Entabeni.

In his initial years, Shaka had neither the influence nor reputation to compel any but the smallest of groups to join him, and upon Dingiswayo's death, he moved southwards across the Thukela River, establishing his capital, Bulawayo, in Qwabe territory. He never returned to the traditional Zulu heartland. In Qwabe, Shaka may have intervened in an existing succession dispute to help his own choice, Nqetho, into power.

As Shaka became more respected by his people, he was able to spread his ideas with greater ease. Using his background as a soldier, Shaka taught the Zulus that the most effective way of gaining power quickly was by conquering and controlling other tribes. His teachings greatly influenced the social outlook of the Zulus. The Zulu tribe soon developed a warrior outlook, which Shaka used to his advantage.