Who is the author of the most prominent book on Yoga, Yog Darshan?

Among the six classical schools of Indian philosophy (Shad-Darshan — Nyaya, Vaisheshika, Samkhya, Yoga, Mimamsa, and Vedanta), Yog Darshan is the school built on Samkhya's dualism of purusha (consciousness) and prakriti (matter); it defines yoga as chitta-vritti-nirodha (stilling the fluctuations of the mind) and sets out a systematic, step-by-step practice toward kaivalya — the discriminative isolation of purusha from prakriti. Its foundational text organizes this philosophy into a compact set of aphorisms (sutras) covering ethical discipline, physical and mental practice, and the stages leading to that liberation.

This foundational text — commonly called the Yoga Sutras or Yog Darshan — was composed by Maharshi Patanjali, traditionally placed around the 2nd century BCE. Patanjali organized the practice into the eight limbs (Ashtanga Yoga): Yama, Niyama, Asana, Pranayama, Pratyahara, Dharana, Dhyana, and Samadhi, making him the recognised author of Yog Darshan.

• Maharshi Bharat — best known as the legendary king after whom Bharatvarsha (India) is named in genealogical/epic tradition, not as the compiler of any philosophical sutra text.

• Maharshi Narad — associated with the Narada Bhakti Sutra, a text on the devotional (bhakti) path composed within its own tradition, distinct from Patanjali's systematic treatise on yoga practice.

• Maharshi Devadatta — a name appearing in Puranic/legendary narratives, not linked to any systematic philosophical treatise on yoga.

Hence, the author of Yog Darshan is Maharshi Patanjali.