The dark-haired man leaning on the block of stone in the center is a depiction of Michelangelo. Raphael had completed this fresco before Michelangelo was half-done with the Sistine Chapel ceiling. After the first half of the Sistine Chapel was completed, there was a big “unveiling” ceremony, and Michelangelo single-handedly raised the bar for Renaissance painters instantly. Raphael was simultaneously impressed and jealous, so he went back into “The School of Athens” and chiseled out a spot for Michelangelo to be in. His depiction of the artist is meant as both a compliment and a curse, as the artist is seen thinking over a block of stone (he had considered himself more a sculptor than a painter).