Kacha (Sanskrit: Kaca) was an ancient sage and the son of Brihaspati in Hindu mythology. The narrative of Kacha is mentioned in the Mahābhārata, the Matsya Purana and the Agni Purana. He was sent by his father Brihaspati to learn the secret of the Sanjivani mantra (a hymn for reviving the dead) from Shukracharya, the guru of the Asuras. The idea was to help the Devas with the knowledge of this secret.
He learned under the sage Shukracharya, who had a daughter Devayani. Devayani falls in love with him. In the meantime the Asuras wanted to kill Kacha. Every time they killed him, Shukracharya revived him with his art. The Asuras finally killed him and mixed his remains with divine water and served it to Shukracharya. Shukracharya unknowingly consumed the divine water, and when he tried reviving Kacha, he realised that Kacha was in his stomach. So he was forced to teach this art to Kacha, who came out tearing open his guru's stomach. Kacha then revived his guru with his newly learnt Sanjivani mantra.
After completion of his education, Devayani asked Kacha to marry her, but he refused on the grounds that she is his sister as he had come out of Shukracharya. She cursed him that he would never be able to use his art again. To this, Kacha replied that he would only not be able to use it, but he would definitely be able to teach it. Thus, Kacha is credited with learning the secret of the Sanjivani mantra from Shukracharya.