Udayana also known as Udayanācārya (Udyanacharya, or Master Udayana) was a very important Hindu logician of the tenth century who attempted to reconcile the views held by the two major schools of logic (Nyaya and Vaisheshika). This became the root of the Navya-Nyāya school of the thirteenth century, established by Gangesha Upadhyaya ("New Nyāya") school of "right" reasoning, which is still recognized and followed in some regions of India. He lived in Kariyan village in Mithila, near present-day Darbhanga, Bihar state, India.
Udayana wrote a sub-gloss on Vachaspati's work called the Nyaya-vaartika-taatparya-tiikaa-parishuddhi. He wrote several other works such as the Kusumanjali, Atma-tattva-viveka, Kiranaavali and Nyaya-parishishhta (also called Bodha siddhi or Bodha shuddhi).
He it is to whom credit is given by Naiyâyikas for having demolished in final fashion the claims of the Buddhist logicians. All his works, or at least all of which we know, have been preserved, which attests to the respect in which he was held from the beginning.