As a younger man, Anakin Skywalker was one of the most powerful Jedi Knights to serve in the Jedi Order. Under the guidance of Obi-Wan Kenobi, Skywalker was a general in the Clone Wars, where he received much acclamation from his peers and superiors. This all changed when Skywalker fell to the dark side of the Force, undergoing a transformation into one of the most powerful Sith Lords that ever lived: Darth Vader.
For the remainder of his life, Darth Vader would serve the Galactic Empire; wiping out the remaining Jedi, establishing Imperial rule and attempting to crush the Rebel Alliance that formed as a result. All the while, Vader honed his renowned talents for the Force, piloting and lightsaber combat to serve the will of the dark Emperor Palpatine, turning his back on everything he once stood for.
Vader was respected and feared throughout the ranks of the Imperial Army (not to mention the rest of the galaxy), and after hearing of his feats of raw strength and skill, it's easy to understand why.
Obi-Wan Kenobi's former apprentice attained a level of infamy second only to the Emperor itself, and he did so by hunting down and killing the surviving Jedi and terrorising the Rebel Alliance - overcoming great odds in the process...