Whizbang Dustyboots
Gnometown Hero
Halband flat-out asked Adar if he recognized him, while furiously holding a spear at Adar's neck.It seems unlikely that Adar was lying about backstabbing Sauron, but we also know Sauron's essence can reform. That points the finger directly at The Stranger.
Sauron is either Halbrand or is riding him in a form of possession, which would explain both Halbrand's savagery back in Numenor (where Sauron was supposed to appear in a fair form) and why Halbrand seems tormented by some of the things he's done (under Sauron's influence).