Kalanemi was a rakshasa (night-wandering demon) who was dispatched by the asura (demon) king Ravana to prevent Hanuman, the monkey god and loyal servant of Rama, from reaching the magic Drona mountain. Hanuman needed healing herbs for the wounded Lakshmana during the Rama-Ravana war. Kalanemi appeared as a brahmin in order to fool Hanuman, but this shape-shifting demon got himself killed in the process.
He also had a lifetime during the Krishna incarnation as Kamsa, the evil uncle of Krishna.