Rashi, Rambam, the Maharal, the Rosh, the Rema, etc. are all usually referred to by their acronyms. This custom makes sense in a culture that is mostly transmitted through the written word where ink and paper were not cheap - someone wrote רש"י, so I say Rashi.
Who was the first person to be generally addressed as an acronym? Who popularized the use of that acronym?