A black knight is a character fictional stories. They are soldiers or knights who do not have a lord, or the lord is secret. They do not have any heraldic standards or have painted them over with black paint. In these stories, black knights are usually evil knights that are good at fighting and usually work alone.
In Arthurian legend Black Knight was a magical knight summoned by Sir Calogrenant. The Black Knight never told his name. He defeated Sir Calogrenant. Later The Black Knight was killed unfairly by Yvain in a act of revenge for his cousin, Sir Calogrenant.