What is "sanatkumara"

Sage Sanatkumara was one of the Four Kumaras, the four Manasputras (mind-born-sons) or spiritual sons of Brahma according to Puranic texts of Hinduism, including the Bhagavata Purana, whose other sons were Sanaka, Sanatana, and Sanandana. Sanatkumara in Sanskrit means "eternal youth". Though in Mahabharata, total seven sons are mentioned, namely: Aniruddha, Sana, Sanatsujata, Sanaka, Sanandana, Sanatkumara, Kapila, and Sanatana and further mentions that,"Knowledge comes to these seven rishis, of itself (without being dependent on study or exertion). These seven are wedded to the religion of Nivritti (inward contemplation). They are the foremost of all persons conversant with Yoga. They are possessed also of deep knowledge of the Sankhya philosophy. They are preceptors of the scriptures on duty and it is they that introduce the duties of the religion of Nivritti (inward contemplation), and cause them to flow in the worlds".

He is also the author of the Sanatkumara Samhita, which is part of the Shiva Purana, and has 59 chapters. It is also taken as a part of the Pañcaratra, Vaishnavite devotional texts.

The Chandogya Upanishad, Chapter seven, is about Sanatkumara's Instructions on Bhuma-Vidya to celestial sage Narada, Sanatkumara finds mention across Mahabharta, as a great sage, who dispels doubts and the preceptor in all matters affecting Yoga

Also mentioned is the Tirtha of Kanakhala near Gangadwara or Haridwar, where through extensive tapas, he attained great ascetic powers.