Raphael used himself as well as Michelangelo and Leonardo (among others) as models for the figures in The School of Athens. The figures pictured represent many of the great Ancient Greek philosophers, scientists and mathematicians. A list of the people pictured can be found on good ol wiki:http://en.wikipedia.org/wiki/The_School_…
Considering that the Renaissance was a time where the ideals and aesthetics of the Ancient world were "reborn", it is fitting that a Renaissance artist like Raphael would pay tribute to the Ancient Greeks in that painting.