Darth Vader's appearance in "Rogue One: A Star Wars Story" was truly a treat for audiences. In the limited screen time that he was given, it marked the first time his powers as a Sith was displayed since his conversion to the Dark side. This marks the question on how Vader develop those powers and his activities between the twenty-year time period.

As Insider puts it, his "Rogue One" appearance is not that of a young and inexperienced Anakin Skywalker, but a mature and disciplined Vader whose Force powers are at its peak. In the few minutes he is in, he makes quick work of the rebels with a combination of his light saber and force powers, without even breaking a sweat. Thanks to the novels and animated series set between the gap, fans may know how his powers and character developed further after Episode III.

A few years after Order 66, Palpatine was working closely with the newly-formed Vader, in his way to make sure he completely cuts off his ties to his former self. As seen in the novel "Star Wars: Lords of the Sith", in one mission, they work together in destroying the insect-like Lyleks in the planet Ryloth. Vader also proves his loyalty to his master by killing everyone in the village that helped them.

He also spends some time with Moff Tarkin, before he takes on the "Grand" title. The 'Star Wars: Tarkin' novel shows how the initially cold Tarkin and Vader start having mutual respect for one another, as they pursue a stolen ship, Tarkin's Carrion Spike, as IGN reports.

"The Star Wars: Rebels" animated series showed more of this baddie, as he directs his Inquisitors to rally up all the force-sensitive children to get them to their cause, or end them. He then meets someone from his past, his former padawan Ahsoka Tano. In their climactic and emotional duel, Vader gets damaged heavily, while Ahsoka's fate was left unknown as their battleground collapsed.

His experience after converting to the dark side was finally culminated in his scenes on "Rogue One". His grandson, Kylo Ren, will also manifest more of his skills in 2017's "Star Wars Episode VIII".