What expansions do I need to use a mercenary?

Mercenaries were introduced with the Seeds of Destruction expansion and you must have that expansion enabled in order to buy a mercenary. The expansion is now available to all players on the regular servers, but may not be available on progression servers that have not yet unlocked the expansion.

In order for mercenaries to gain their own experience and alternate abilities, and to be able to equip their special gear, you must have the Call of the Forsaken expansion.