BioWare's lead designer James Ohlen has done a quick interview with IGN about Star Wars: The Old Republic's concept of "companion characters." Not only do you get to tool around the universe as a Sith or a Jedi, but as we first heard back at the game's announcement, you get to bring some other poor suckers with you. The idea sounds a lot like your party members from Dragon Age or Mass Effect 2 -- your companions will follow an "Affection" system, and you can end up making them "twisted to the dark side of the Force" or "stronger and more independent," depending on how you treat -- even gift -- them. (Those being just a couple of examples.)
Companion characters will also have a lot of combat utility, and you may want to bring some of them based strictly on how they complement you in combat. The gear you equip for them will also make a difference, so you may have to tailor your party and their gear for the specific goals of any given mission. The system doesn't sound too different from past BioWare games, with the caveat that, since it's an MMO, you'll have to direct AI players in real-time rather than pausing the game to give out orders. Ohlen also says his favorite recent character is Alistair, which worries us a little bit -- he always struck us as whiny.