Why is the Kongo kingdom spelled with a K but Congo River C?

The Kongo kingdom is spelled with a "K" because it is the original spelling of the name of the kingdom in the Kongo language. When the Portuguese explorers first arrived in the region in the 15th century, they spelled the name of the kingdom as "Congo", but this spelling was later changed to "Kongo" to reflect the original pronunciation. The Congo River is spelled with a "C" because it is the English spelling of the name of the river. The word "Congo" comes from the Portuguese word "congo", which is thought to have come from the Kongo language word "nkôngo", meaning "hunter".