From Star Wars: The Old Republic Wiki
Companions are NPCs that accompany players during gameplay, the first being acquired while on the player's starting planet. Each class can unlock five unique companions over the course of the game in addition to a generic ship droid companion. Companions provide commentary, combat support depending on their specialization, and perform Crew Skills, each having unique bonuses. They gain or lose affection depending on conversation choices and by receiving gifts. Some companions are romance options. To speak with your companions in private and accomplish their individual missions, simply take them to a resting zone.
 Known companions
 Galactic Republic
RF denotes female character romance option, RM denotes male character romance option.
 Sith Empire
 Companion Gifts
You can give your companions gifts, which improve their performance in combat and on crew skill missions. Each companion has gift preferences, which are detailed on the Companion Gifts page.
 See also
 External links
Official companions page on swtor.com