Dharmnath Bhagwan was the fifteenth Tirthankara in Jainism. According to Jain tradition, each Tirthankara delivers the first sermon (Divya Dhwani) after attaining omniscience (Kevalgyan), and their first chief disciple is called the "Ganadhar" or "Gandharva."

For Shri Dharmnath Bhagwan, his first Gandhar (chief disciple) was Shri Sanku. This information is found in various Jain texts that list the Tirthankaras along with their Yaksha-Yakshini, Gandhar, and other details.

So, Shri Sanku was the first Gandhar of Dharmnath Bhagwan.