Alpha Roar is the ability to transform a shapeshifter into it's human or beast form. Many supernatural creatures have the ability to roar though very few can use it to affect others. Werewolves can roar to signal and call out to each other whether they are part of a pack or not, Alphas however, can inspire or dominate another werewolf by roaring at them, the werewolf will then either find newfound strength or can be forced to shape-shift. This is not exclusive to werewolves as their werecoyote cousins are able to be affected by an Alpha's roar.
Alpha Werewolves are the only supernatural beings seen to use this power. By unleashing a roar, they are able to turn a werewolf back into their human form against their own will. This power does not work on other Alphas.