Bellur Krishnamachar Sundararaja Iyengar (Kannada: ಬೆಳ್ಳೂರ್ ಕೃಷ್ಣಮಾಚಾರ್ ಸುಂದರರಾಜ ಐಯಂಗಾರ್, Tamil: பெல்லூர் கிருஷ்ணமாச்சார் சௌந்தரராஜா ஐயங்கார்), (known as 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 yoga practice and philosophy, and is best known for his books Light on Yoga, Light on Pranayama, and Light on the Yoga Sutras of Patanjali. Iyengar yoga classes are offered 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. In 2004, Iyengar was named one of the 100 most influential people in the world by Time Magazine.

B.K.S. Iyengar was born into a poor Iyengar family. He was the 11th of 13 children of father Sri Krishnamachar, a school teacher, and mother Sheshamma. Iyengar's home village of Bellur, in Karnataka, was in the grips of the influenza pandemic at the time of his birth, leaving him sickly and weak. Throughout his childhood, he struggled with malaria, tuberculosis, typhoid fever, and general malnutrition. Iyengar's father died when he was 9 years old.