In the original version of Final Fantasy XIV, Path Companions were paired members of the Path of the Twelve, an organization of people touched by the Echo. They were partners in all missions given by this organization, and it was frowned upon to rush into dangerous missions alone if you have one.
At the onset of the fifth main scenario quest, players were presented with the opportunity to select an NPC Path Companion to join them in the search for truth behind the mysteries surrounding Eorzea. Players were faced with several important decisions when selecting the companion just right for them. After deciding on a class and nickname, players also selected the race and gender of their companion. The personality of the NPC varied greatly depending on race and gender.
Initially, it was impossible to change your Path Companion, forcing players to delete and recreate their characters wholesale if they didn't like their choice. However, early patches to the game granted the ability to select a new one.
At one time, it was rumored that players would be able to call their Path Companions in the field, much like the Adventuring Fellow NPCs in Final Fantasy XI.
Path Companions were completely removed in FFXIV's Realm Reborn update. Even Legacy characters no longer possess the ability to call their companions, and no indication has been given that the feature will return.