Historically, crippled veteran templar could volunteer to continue serving by being transplanted into dragoon exoskeletons. This honored tradition was broken when the zerg infested the sacred shrine dedicated to the creation of dragoons during the fall of Aiur. After the Brood War, crippled protoss soldiers were transplanted into the new immortal shells.
Immortals are outfitted with twin phase disruptors as their primary attack form; they give critical fire support to legions of zealots. Their specially hardened energy shields only activate when struck by powerful attacks, which leaves them more vulnerable to the pinprick attacks of lesser foes. (more...)