Five

1. Shri Shankaracharya Shankara Incarnation of Shiva (Sky)
2. Shri Nimbakacharya 4Kumars Incarnation of Chakra (Hell Earth Heaven )

3. Shri Ramanujacharya Ramanujacharya Incarnation of Adhi Shesha (Water)

4. Shri Madhvacharya http://8mad.blogspot.com/  Incarnation of Vayu (Air)
5. Shri Vallabacharya Valab  Incarnation of  Agni (Fire)