 Most popularly, this worship takes the form of singing Radha and Krishna's holy names, such as "Hare", "Krishna" and "Rama", most commonly in the form of the Hare Krishna (mantra), also known as kirtan.It sees the many forms of Vishnu or Krishna as expansions or incarnations of the one Supreme God, "adipurusha".After its decline in the 18-19th century, it was revived in the beginning of the 20th century due to the efforts of Bhaktivinoda Thakur.