SB 10.1.68
atmanam iha sañjatam
janan prag visnuna hatam
mahasuram kalanemim
yadubhih sa vyarudhyata
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
In his previous birth, Kamsa had been a great demon named Kalanemi and been killed by Visnu. Upon learning this information from Narada, Kamsa became envious of everyone connected with the Yadu dynasty.
Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
Persons who are demons, enemies of the Supreme Personality of Godhead, are called asuras. As stated in Bhagavad-gita, the asuras, because of their enmity toward the Supreme Personality of Godhead, take birth after birth in asura families and therefore glide down to the darkest hellish regions.