Shri Krishna: Shri Raama, the reincarnation of Lord Narayana.

Rukmini: Seeta, the reincarnation of Goddess Mahaalakshmi.

Bheemasena: Hanumanta, the reincarnation of Lord Vayu

Balaraama: He was Lakshmana - the brother of Lord Raama who was like His shadow throughout Raamaayana. He was basically a reincarnation of Lord Shesha - the celestial seven headed serpent who serves as Lord Naaraayana’s bed.

Arjuna: he was the ape king Vaali in Raamaayana - who was killed by Lord Raama. He was an incarnation of Indra. He had earned great demerit by serving Raavana as his ally during Ramayana.

Karna: Sugreeva in Raamaayana, incarnation of Sun. He had an amsha of a demon by name Sahasravarman. Due to the demonic influence he insulted Draupadi.

Draupadi: She was Indrasenaa a.k.a Nalanandini, the daughter of Nala and Damayanti in her previous birth. She carried the bearer soul of Bhaarati devi, the divine spouse of Lord Vayu who carried souls of Shyamala devi (wife of Yama Dharma), Shachi (wife of Indra), Usha Devi (wife of Ashwini Twin Gods - Drasu and Nasatya) and Paarvati (wife of Lord Rudra). You may read the following answer of mine which entails the birth of Draupadi.

Anandteerth Deshpande's answer to How was Draupadi born?

Drona: He was Brihaspati reborn. He was not an incarnation but had an amsha of Lord Brahma because of which he never asked anything in daana from anyone other than Lord Narayana’s incarnations. That’s why he went seeking a cow only from Parashuraama. No - he did not ask anything from his friend Drupada.

Kripi (the wife of Drona): Taaraa - wife of Brihaspati.

Drupada: He was a Gandharva by name Huhu in his previous birth and carried the essence of a Marut God by name Aavaaha.

Bheeshma: He was one of the eight God brothers by name Ashtha Vasus. His name was Dyu and was also known as Prabhaasa. He was born to fulfill the curse of Lord Brahma.

Shikhandi: he was born as Shikhandini but became a man later. He was earlier Amba, the princess of Kaashi. Amba was Varaangi, the wife of Prabhaasa who took birth as Bheeshma later. So - by divinity both Amba and Bheeshma were soulmates never to be unified due to curse of Brahma. Moreover, Varaangi was cursed to be the reason for her husband’s death.

Shaantanu: He was King Mahaabhishak in his previous birth. Originally he was Lord Varuna - the lord of rains and waters. Lord Varuna is also the divine husband of Goddess Ganga.

Yudhishthira: He was the reincarnation of Yamadharma.

Vidura: He was the incarnation of Yamadharma born to fulfill the curse of Sage Mandavya.

Paandu: He was among 12 Maruta Gods, by name Paraavaha.

Kunti: Siddhi - wife of the Marut God - Paraavaha

Abhimanyu: He was the son of Vaali - Angad in Raamaayana who was loyal to Lord Raama.

Nakula and Sahadeva: Both were Ashwini Twin Gods by name - Draasu and Nasatya.

Pradyumna, the son of Lord Krishna: He was Lord Raama’s brother Bharata in his previous life.

Aniruddha, the son of Shri Krishna: He was Lord Raama’s brother Shatrughna in Raamaayana.

Bahleeka, the brother of Shaantanu: was Prahlaada - the son of Hiranyakashipu who was the reason why Lord Narayana took birth as Narasimha. Prahlaada was a God named Shankukarna who was cursed to take birth on earth, by Lord Brahma once when he was delayed to fetch flowers for Lord Brahma who was to worship Lord Narayana.

Devaki, mother of Lord Krishna: She was Aditi, the wife of Sage Kashyapa.

Rohini, mother of Balaraama: She was Surabhi, another wife of Sage Kashyapa

Vasudeva, father of Lord Krishna: He was Sage Kashyapa.

Dhritaraashtra: Was a Gandharva by name: Hamsa.

Dhristadyumna: he was Agni incarnate.

Shishupaala: He was Raavana in his previous birth. He is originally Jay - a gatekeeper of Lord Narayana’s abode - Vaikuntha.

Dantavakra: He was Kumbhakarna in his previous birth. He is originally Vijaya - another gatekeeper of Lord Narayana’s abode - Vaikuntha.

Kripaacharya: Vishkambha - one of the eleven Marut Gods.

Shakuni: Dvaapara - he was symbolic of Dwaapara Yuga’s slightly accentuated acceptance of evil and dichotomy of truth.

Duryodhana: the most evil demon: Kali.

Duhshyaasana: He was the son of Raavana, Indrajit (also known as Meghnaath by many in North India) in his previous birth.

Vikarna: The demon - Atikaaya.

Duhshalaa, the only sister of Kauravas: She was a demoness by name: Mrishaa

Keechaka: The demon - BaaNaasura

Jaraasandha: The second most evil Demon after Kali - Viprachitti.

Shrigaala Vaasudeva, half brother of Lord Krishna: He was a demon - Dundhu

Paundraka Vaasudeva, another evil half brother of Lord Krishna: He was a demon by name Vena.

Pootanaa, the demoness and nanny of Kamsa: She was TaaTakaa, the demoness who was killed by Lord Raama in her previous birth. Actually she was the apsara - Oorvashi who was bearing a curse to take births as demoness.

Kamsa: He was a demon by name Kaalanemi

Ugrasena, the father of Devaki and Kamsa: was a Gandharva singer of the same name.

Ghatotkacha: He was a dikpaalaka by name: Nirruti.

Ashwatthaama was Lord Shiva born as the son of Drona who had the amsha of Lord Brahma. In reality Lord Shiva is the son of Lord Brahma.

All 100 Kauravas and their sister were demons in their previous births...

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