根据主从句时态呼应原则,应该是:
Who is the cleverest person in the world that has ever lived? (此人可能仍然健在,也可能已经去世)
Who was the cleverest person in the world that had ever lived?(此人已经去世)
《高考英语备考1号·速效编》
《高考英语备考1号·写作编》
《高中英语晨读晚记》
《高中英语错题笔记》
《零起点考大学英语》