While to follow Vader's battles, the experience of living under the Empire created a very different impression than the one fans know, turning him into a boogeyman who haunted the nightmares of the most powerful people in the galaxy.
With many different cultures and species, Star Wars' galaxy is a place of grand symbolism, with ideas often being reduced down in order to be understood by all. It's for this reason that the Jedi Order was able to spread its message of hope, but it's also how Palpatine's post-Order 66 slander took hold. Ultimately, most normal people in Star Wars are hearing about events happening worlds away. In that context, it's easy to see how in destroying Alderaan and slaying countless Jedi, Darth Vader would come to represent something even more imposing than he actually is.
The purest example of this is seen in Star Wars: Darth Vader #25 (from Kieron Gillen and Max Fiumara). After returning to Tatooine for the first time since he left as Anakin Skywalker, Vader repeats his previous massacre of the Tusken Raiders, destroying an encampment. The story 'Coda' shows the rest of their society discovering the slaying, with a surviving raider telling the story of Vader's attack. However, in the retelling Vader goes from a Sith Lord to a dark god. He's recalled as a towering black shape who slew dozens with a single slice of his blade, and even tore a star out of the sky in order to fashion it. The issue ends with the Tusken Raiders building a pyre to Darth Vader and sacrificing the survivor, hoping to ward off what they consider to be a towering supernatural threat.
How the Tusken Raiders See Darth Vader
While it's easy to see this as the misunderstanding of a group who don't comprehend Tusken Raiders may exaggerate his methods, they're utterly correct about his capabilities.
Especially under Palpatine, the Sith ruled through fear, and Darth Vader was as much a threat the Empire levied against its agents as he was an actual individual. The god the Tusken Raiders imagine when they see Vader's handiwork isn't a physical reality, but the statement it makes about him is. While fans may know that Darth Vader is a tragic former Jedi enhanced with mechanical upgrades, the Star Wars galaxy perceives him as something more - an inexplicable force of evil, devoid of an origin and - it seems from his actions - any mercy, weaknesses, or limitations. Darth Vader may not be a god, but as the Tusken Raiders concluded, his destructive potential means he might as well be.
