Very systematic processes of yoga were written by great Sage Patanjali in 500BC. He wrote Yoga Sutras to explain the process and systematic analysis of practical methods for awakening and expanding the higher faculties of mind, intellect, quality of consciousness. His path of Ashtanga yoga included yamas and niyamas, Asanas, Pranayama, Pratyahara, Dharana, Dhyan, Samadhi. Yoga Sutras are concisely packed 196 lines in Sanskrit which are divided into 4 chapters.
Shankaracharya - A revolutionary Yoga Master who lived in 800 AD, re-energized the yoga culture. He united various yoga traditions, sorted the ideological differences and gave science of yoga a wider appeal. He wrote commentaries on Bhagavad Gita, Upanishads, Vedant philosophy, which are wonderful insights in to science of yoga. He founded the tradition of Swami Sannyasa or monks who played a very positive role in society after that.