The School of Athens

The School of Athens is a famous fresco by the artist Raphael. It was painted during the Italian Renaissance between 1510 and 1511. The picture is known as "Raphael's masterpiece and the perfect embodiment of the classical spirit of the High Renaissance".
It was painted as a part of Raphael's commission to decorate with frescoes the rooms now known as the , in the Apostolic Palace in the Vatican. 
Figures.
Only the identities of some of the philosophers in the picture, such as Plato or Aristotle, are certain.
A proposed list of possible identifications, is the following:
1: Zeno of Citium
2: Epicurus Possibly, the image of two philosophers, who were typically shown in pairs during the Renaissance: Heraclitus, the "weeping" philosopher, and Democritus, the "laughing" philosopher.
3: unknown (believed to be Raphael)
4: Boethius or Anaximander or Empedocles?
5: Averroes
6: Pythagoras
7: Alcibiades or Alexander the Great?
8: Antisthenes or Xenophon or Timon?
9: Raphael, Fornarina as a personification of Love or Francesco Maria della Rovere?
10: Aeschines or Xenophon?
11: Parmenides? (Leonardo da Vinci)
12: Socrates
13: Heraclitus (Michelangelo)
14: Plato (Leonardo da Vinci)
15: Aristotle (Giuliano da Sangallo)
16: Diogenes of Sinope
17: Plotinus (Donatello?)
18: Euclid or Archimedes with students (Bramante?)
19: Strabo or Zoroaster? (Baldassare Castiglione)
20: Ptolemy?
R: Apelles (Raphael)
21: Protogenes (Il Sodoma, Perugino, or Timoteo Viti)