I can't say who is the most powerful - I haven't read, played or watched every story! But I would say characters like Darth Sidious, able to take down two lightsaber wielding, fearsome opponents such as he did, killing one, is very powerful indeed. Possibly inducing dark future dreams for Anakin, urging Anakin to kill his own apprentice, or Dooku to kill his. Urging Luke to kill his own apprentice, or torturing him, likely to the point of death, after he made his decision. Then, there's obviously Vader, able to destroy a room full of Rebels, using the Force and a lightsaber very effectively. Taking on his former apprentice, while both seemed to perform rather well, despite one ending up, at one point, better than the other. Or, killing an Imperial from an incredibly far distance, or matching his Master Obi-Wan in battle. But, what do you think? Of canon characters, Legend characters, all mediums, who're the most powerful - and why?