Bellur Krishnamachar Sundararaja Iyengar (Kannada: ಬೆಳ್ಳೂರ್ ಕೃಷ್ಣಮಾಚಾರ್ ಸುಂದರರಾಜ ಐಯಂಗಾರ್), (also known as Yogacharya B.K.S. Iyengar) (Born December 14, 1918 in Bellur, Kolar District, Karnataka, India) is the founder of Iyengar Yoga. He is considered one of the foremost yoga teachers in the world and has been practicing and teaching yoga for more than 75 years. He has written many books on yogic practice and philosophy, and is best known for his books Light on Yoga, Light on Pranayama, and Light on the Yoga Sutras of Patanjali. He has also written several definitive yoga texts. Iyengar yoga centers are located throughout the world, and it is believed that millions of students practice Iyengar Yoga.

He was awarded the Padma Shri in 1991, and the Padma Bhushan in 2002.

B.K.S. Iyengar was born into a poor Hebbar Iyengar family. He had a difficult childhood. Iyengars home village of Belur, Karnataka, India, was in the grips of the influenza pandemic at the time of his birth, leaving him sickly and weak. Iyengars father died when he was 9 years old, and he continued to suffer from a variety of maladies in childhood, including malaria, tuberculosis, typhoid fever, and general malnutrition.

At the age of 15 Iyengar went to live with his brother-in-law, the well-known yogi, Sri Tirumalai Krishnamacharya in Mysore. There, Iyengar began to learn asana practice, which steadily improved his health. Soon he overcame his childhood weaknesses.

With the encouragement of Krishnamacharya, Iyengar moved to Pune to teach yoga in 1937. There his practice developed as he spent many hours each day learning and experimenting in various techniques. As his methods improved, the number of students at his classes increased and his fame spread. In Pune, his brothers introduced him to Ramamani, whom he married in 1943.

In 1952, Iyengar met and befriended the famous violinist Yehudi Menuhin. Men