In Jainism, Buddhism and Hinduism, a sādhaka is someone who follows a particular sādhanā, or a way of life designed to realize the goal of one's ultimate ideal, whether it is merging with brahman or realization of one's personal deity. The word is related to the Sanskrit sādhu, which is derived from the verb root sādh-, 'to accomplish'. As long as one has yet to reach the goal, they are a sādhaka, while one who has reached the goal is called a siddha. In modern usage, sadhaka is often applied as a generic term for any religious practitioner. In medieval times it was more narrowly used as a technical term for one who had gone through a specific initiation.
Hindu, Jain, and Vajrayana Buddhist traditions use the term sadhaka for spiritual initiates and/or aspirants.