Kudeyar (Russian: Кудеяр) is a legendary robber, a Russian folk hero.

There were several Cossack robbers of this name. There is a letter of one Muscovite boyar to Ivan IV from Crimea, where he reports that "there is only one brigand left here - the accursed Kudeyar".

According to one legend, Kudeyar was the elder brother of Ivan the Terrible. His mother purportedly was Solomonida Saburova, whom Vasily III divorced on account of her barrenness and incarcerated in a convent. Several months after the controversial divorce she bore a son, who was smuggled to the Cossacks living along the Don River, where he became their fearless ataman and champion in the manner of Robin Hood.

Kudeyar's story is told in Mykola Kostomarov's 1875 historical novel of the same name.

There are other literary works involving Kudeyar.