Even though he has retired from IIT Madras, I would like to name V. Balakrishnan sir from the Physics Department as the answer to this question. He is one of the most respected faculty members of all time at IIT Madras.
Sir’s knowledge of Physics is unparalleled. It is absolutely stunning how he used to link the seemingly disparate aspects of the natural world. You can watch his lectures on Classical Mechanics on NPTEL and Youtube. Sir acknowledged and answered the queries of all his students. Not only that, he took those simple questions and slightly modified them, thus leading his students to understand deep and profound concepts.
Sir’s classes ignited new thoughts in his students’ minds, and led them to those answers which they never realized they needed. No one wanted to miss any of his classes, which speaks volumes about his teaching.
My brother went to IIT Madras and according to him, all professors are intellectual powerhouses. Here are some of his personal favorite professors in no particular order:
Hope this helps.