Aelan is a former High Elf/Blood elf. He faced the Lich King in battle, after leading a group of elven warriors into certain death at Ebon Hold. Aelan was killed, only raised to suffer even more, after sending most of the scourge undead back to their grave at Ebon Hold. Since he is raised straight after his death, then his organs still are functioning, the necromanic energies ain't exactly keeping his body alive, but they are keeping his organs alive, making the blood circulating as it should. Due to the necromanic energy that strengthen his organs, then he is still able to survive for many centuries, if not forever, until he is killed.