Quoting from my article on Dhanvantari- http://www.newsgram.com/dhanvantari-the-father-of-ayurveda/
Dhanvantari: The incarnation of Lord Vishnu
According to Puranas, when Devas (gods) and Asuras (demons) churned
the ocean for Amrita (nectar of immortality), it was Lord Dhanvantari
who came out of the ocean with a pot of Amrita. Thus, Dhanvantari is
clearly a lord who grants long life and immortality. Bhagavata Purana
(2.7.21) calls Dhanvantari as God himself, who is a curer of diseases,
who has imparted to the world the knowledge of long life i.e.
He is often represented as a God with four hands (similar to Vishnu)
carrying Shankha (conch), Chakra (disc), leech, and a pot containing
Amrita. Leeches play an important role in Ayurvedic treatment.
Therefore, in Hindu tradition Lord Dhanvantari represents twin aspects
of curer of diseases and a granter of long life and immortality. Thus,
he is clearly identified with all aspects of health, medicine, and
Dhanvantari: The teacher of Ayurveda
Apart from Lord Dhanvantari who is the personification of health
itself, the Bhagavata Purana and Ayurvedic tradition speak about at
least two other Dhanvantari who lived and practiced Ayurveda at
different periods. Bhagavata Purana (9.17.4) speaks about a
Dhanvantari (also Adi-Dhanvantari) who was the son of Dhirgatama in
the Pururava dynasty. It describes this person as an incarnation of
Vishnu and as the inaugurator of the knowledge of Ayurveda.
This Adi Dhanvantari is believed to have divided Ayurveda into eight
divisions: Kayacikitsa (Internal Medicine), Kaumarabhrtya
(Pediatrics), Bhutavidya (Psychiatry), Salakyatantra
(Otto-Rhino-Laryngology & Ophthalmology), Salyatantra (Surgery), (vi)
Visatantra (Toxicology), (vii) Rasayanatantra (Geriatrics), (viii)
Vajikaranatantra (The therapy for male sterility)
Another person who is identified as Dhanvantari is Divodasa, the
great-grand son of Adi-Dhanvantari (the son of Dhirgatama). He is
believed to have been living around 3000 BC, according to some
scholars. Divodasa Dhanvantari was the teacher of Susruta, the famous
Ayurvedic physician and is prominently mentioned in the
Divodasa Dhanvantari has made enormous contributions to Ayurveda.
Though, he has not written any Ayurvedic treatise, his teachings could
be seen through Susruta-Samhita. He was responsible for the division
of Ayurvedic surgery into two main branches: Salyatantra and
Salakyatantra. He has given extensive lectures on methodology and
intricacies of surgery, which has been recorded by Susruta.
Regarding surgery, Divodasa Dhanvantari instructed Susruta thus: “Hear
me discourse on the science of surgery (Salyatantra) which is the
oldest of all the branches of Ayurveda… All hold this tantra to be the
most important of all the branches of Ayurveda inasmuch as
instantaneous effects can be produced with the help of such measures
as surgical operations, external application of Ksaras
(alkalies/caustics), cauterisation, etc., and inasmuch as it contains
all that can be found in other branches of Ayurveda as well.”
Agnivesasamhita also makes several references to the views of Divodasa
Apart from this, Brahmavaivarta Purana also mentions one Dhanvantari who was among the 16 students who learned Ayurveda from Lord Bhaskara (Surya). And there was one Dhanvantari among the 9 gems of Vikramaditya.
The Human teacher, Adi Dhanvantari is an incarnation of Lord Dhanvantari, the God. That is how, this must be understood.