My brother attended IIT BHU. According to him, the most famous successful alumni of IIT BHU is P.M. Ajayan who pursued B.Tech in Metallurgical Engineering in the year 1985. 

He is a Guinness World Record holder scientist and is currently working as a professor at Rice University Houston Texas USA in the Mechanical Engineering and Materials Science Department. 

Before Rice University, he was the director of the NYSTAR interconnect focus center atRensselaer Polytechnic Institute till the year 2007 and was also the Henry Burlage Professor of Material Sciences and Engineering.