Step 1: Understanding the Concept:
The question asks to identify the Guru (teacher) of the eminent Hindustani classical vocalist, Pandit Omkar Nath Thakur.
Step 2: Detailed Explanation:
Pandit Omkar Nath Thakur (1897-1967) was a celebrated vocalist of the Gwalior Gharana. He was a principal disciple of Pandit Vishnu Digambar Paluskar, a visionary musician and musicologist who founded the Gandharva Mahavidyalaya. Paluskar played a pivotal role in popularizing classical music among the masses.
Step 3: Final Answer:
Pandit Omkar Nath Thakur was the disciple of Pandit Vishnu Digambar Paluskar.