Dhanteras, also known as Dhanatrayodashi , is the first day that marks the festival of Diwali in India. It is celebrated on the thirteenth lunar day of Krishna Paksha (dark fortnight) in the Hindu calendar month of Kartik. Dhanvantari, who is also worshipped on the occasion of Dhanteras.
Dhanteras is the worship of lord Dhanvantari. Lord Dhanvantari, according to Hindu Mythology, emerged during Samudra Manthan, holding a Kalasha full of Amrit (an Ayurvedic herbal mix bestowing immortality) in one hand and the sacred text about Ayurveda in the other hand. He is considered to be the Vaidya of Gods.