- "Whomsoever takes up this blade shall wield power eternal. Just as the blade rends flesh, so must power scar the spirit."
- —The inscription on Frostmourne's pedestal
There were thousands of souls contained in the blade, most notably Terenas Menethil II, Uther the Lightbringer, Archmage Antonidas and King Anasterian Sunstrider. Arthas' own soul was the first it claimed.
Frostmourne is capable of stealing life from it's victims, as well as their souls. The Lich King is capable of seeing through the eyes and hears through the ears of anyone who wields the blade, and he can telepathically communicate with the wielder, which allows him to corrupt them at a distance.
As long as the wielder is within one mile of the blade, he or she is under the complete control of the blade and may not even realize it.
The Lich King can take control of a soulless body that comes in contact with him and Frostmourne at the same time. Unless it willingly merges, the soul within the blade is destroyed, lost forever. If a soul merges with the Lich King, he gains all the skills and memories of the victim. This was done only once, with Arthas Menethil.