The River Congo got its name from the Kingdom of Kongo which was situated on the left banks of the river estuary. The kingdom is in turn named for its Bantu population, in the 17th century reported as Esikongo. South of the Kongo kingdom proper lay the similarly named Kakongo kingdom, mentioned in 1535. Abraham Ortelius in his world map of 1564 labels as Manicongo the city at the mouth of the river. The tribal names in kongo possibly derive from a word for a public gathering or tribal assembly.
The name Zaire is from a Portuguese adaptation of a Kikongo word nzere , a truncation of nzadi o nzere ("river swallowing rivers"), The river was known as Zaire during the 16th and 17th centuries; Congo seems to have replaced Zaire gradually in English usage during the 18th century, and Congo is the preferred English name in 19th century literature, although references to Zahir or Zaire as the name used by the natives (i.e. derived from Portuguese usage) remained common.
The Democratic Republic of the Congo and the Republic of the Congo are named after it, as was the previous Republic of the Congo which had gained independence in 1960 from the Belgian Congo.
The state of Zaire during 1971–1997 was also named after the river, after its name in French and Portuguese.