Sadhaka is derived from the root word, sadh, meaning "to accomplish." Once the sadhaka reaches their goal, they transform into a siddha, or "one who is accomplished." In yoga, a sadhaka is a yogi devoted to the practice of yoga, seeking liberation deep inside the soul.
According to B.K.S. Iyengar, one of the most famous yoga teachers of all time, a sadhaka uses yoga to gain knowledge, light and liberation. It also helps to purify the body and soul.