In the upper right corner is Mirana Nightshade Tyrande of the Night Elf.
On the lower left is the orc leader Thrall.
On the lower right is Kel 'Thuzad, the little lich of the undead (not the Lich King).
This statement is correct. Judging from the characters' images, the one on the upper left is really a little A. If his words are confirmed, then the others are heroes of all ethnic groups.