Radha (IAST: Rādhā, Hindi: राधा ), also called Radhika, Radharani and Radhikarani, is a Hindu goddess who is almost always depicted alongside Krishna and features prominently within the theology of today's Vallabha and Gaudiya Vaishnava sects, which regards Radha as the original Goddess or Shakti. Radha is also the principal god of worship in the Nimbarka Sampradaya, as Nimbarka, the founder of the tradition, declared that Radha and Krishna together constitute the absolute truth. Radha is the most important gopi in Raas (Special kind of dance) with Lord Krishna. Radha is often referred to as Rādhārānī or "Radhika" in speech, prefixed with the respectful term 'Srimati' by devout followers.  Gaudiya Vaishnavas, believe that in fact Radha is the original source from whom Goddess Lakshmi emanated.
Brooklyn Museum - Radha Pining for Her Beloved Page from a dated Rasikapriya Series
In the Vaishnava devotional or bhakti traditions of Hinduism that focus on Krishna, Radha is Krishna's friend and advisor. For some of the adherents of these traditions, her importance approaches or even exceeds that of Krishna. She is considered to be his original shakti, the supreme goddess in both the Nimbarka Sampradaya and following the advent of Chaitanya Mahaprabhu also within the Gaudiya Vaishnava tradition. Radha Chalisha mentions that Krishna accompanies one who chants " Radha" with pure heart. Other gopis are usually considered to be her maidservants, with Radha having the prominent position of Krishna's favour. It has been mentioned in the narration of the Skanda Purana that out of a billion of gopis, 16,000 are prominent. Out of these, 108 are important, and out of 108, eight are principal. Out of eight gopis, Radha and Chandravali are chief, and out of these two Radha is superior. Radharani's superiority is given by Krishna's flute, which repeats the name Radha. Between Radha and Rukmini, Radha is superior, it is also said that when lord Krishna brought all his consorts to meet with goddess Radha they saw Radha rani's face and told that she is the most beautiful lady in the whole universe and she will be there on this position until the end of the universe as no will born more beautiful than her. All the gopis and queens of Lord Krishna are reincarnation of goddess Lakshmi but Radha is the eternal life energy of lord Vishnu. She is greater than goddess Lakshmi as lord Vishnu touches the feet of her.
Her connection to Krishna is of two types: svakiya-rasa (married relationship) and parakiya-rasa (a relationship signified with eternal mental "love"). The Gaudiya tradition focuses upon parakiya-rasa as the highest form of love, wherein Radha and Krishna share thoughts even through separation. The love the gopis feel for Krishna is also described in this esoteric manner as the highest platform of spontaneous love of God, and not of a sexual nature.
Proponents of the Gaudiya and Nimbarka schools of Vaishnavism give the highly esoteric nature of Radha's relationship to Krishna as the reason why her story is not mentioned in detail in the other Puranic texts.
Barsana and Vrindavan in Mathura District, Northern India contain a large number of temples dedicated to both Radha and Krishna, including the Radhavallabh Temple. Sri Sri Radha Parthasarathi Mandir in Delhi is also the Radha krishna Temple.
^Radha in Hinduism, the favourite mistress of Krishna. In devotional religion she represents the longing of the human soul for God: The Oxford Dictionary of Phrase and Fable, 2006, by ELIZABETH KNOWLES
^Kinsley, D. (2010). "Without Krsna There Is No Song". History of Religions12 (2): 149. doi:10.1086/462672. Retrieved 2008-05-03."Nimbarka seems to have been the first well-known religious leader to regard Radha as central to his cult (thirteenth century)"