Who is Su Shi and Su Mi?

It's Mi Fei, because Su Shi and Mi Fei are both Song Sijia, and people call them Misu, which shows that they have profound attainments in calligraphy. The following is the information I found, please refer to:

Mi Fei (1051-1107), a friend of Su Shi, is good at poetry, calligraphy and painting, and is good at collecting places of interest. Both Su Mi are excellent calligraphers. Together with Cai Xiang and Huang Tingjian, they are called "four famous calligraphers" in Song Dynasty.