Kabandha, also called Vishvavasu, was the Gandharva Danu who received the boon of invincibility from Brahma. He became cocky and arrogant.
With his vajra (thunderbolt) Indra hit his head into his stomach and made him a demon.
Rama and Lakshmana killed him, which leads to his redemption and he became a Gandharva again. He helped Rama in the Ramayana.