Sukracharya - how he became guru of asuras (demons-rakshasas) and how he knew the art and science of Sanjivini?

He was the son of Bhrgu Maharshi.He was one of the ancestors of Sri Krishna, his daughter Devayani was the mother of Yadu. He was a son-in-law of Indra. He was the author Sukra Niti and was quoted by Chanakya. Having all these greatest qualifications, how he became guru of asuras ?
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