Who?

During early British times, he instituted a practice (which though around, since Humayun’s time was rarely enforced) that sati had to be completed in the presence of an official. In fact he himself wed a woman whom he rescued from her first husband's pyre. His tombstone – still around in Kolkata’s St. John’s church was constructed with a special type of foliated metamorphosed igneous rocks, which was named after him, retrospectively. Who are we talking about?