The Star Wars universe has been filmed with shining examples of heroes and terrifying examples of villains, but when it came to a truly terrifying physical threat, none could compare to that of Darth Vader's presence. From the moment Anakin was given the suit, and he was sent to earn his place by Palpatine's side, he used his rage to tear through the galaxy with the might of the Empire, but as his story has continued to unfold, it has become even more clear that his first live-action appearances in the Original Trilogy may have shown Vader at his weakest.
In A New Hope, Darth Vader didn't show much of his physicality, but his presence was enough to send chills down the spine of anyone who crossed him. Even the murder of Captain Antilles set a precedent that this person was not to be trifled with. However, in The Empire Strikes Back and Return of the Jedi, something different had affected him -- he learned he had a son. From that point forward, Vader's allegiance to the Emperor became a secondary focus behind his trying to find his son. While he would attempt to kill him when they met on many occasions, there was no doubt that Vader had felt conflict. As a Sith, he felt turning Luke to his side was easier than facing the Light, but eventually, he returned to the Anakin he once was.
Vader always had his physical strength and connection to The Force, but his ruthlessness wavered heavily in the Original Trilogy. This became more prevalent with films like Rogue One: A Star Wars Story and shows like Obi-Wan Kenobi and Star Wars Rebels. In those projects, Vader was ruthless and, as Kenobi put it, "more machine than man." He completed his objectives and used torture and murder to convey his point. Even during his comic runs, Vader acted more like a powerful wall who rarely spoke but used his actions to convey how he felt. However, when he used his actions, it was often to kill or destroy anyone who stood in his way or tried to usurp his command.
Even the Emperor felt that Vader was no longer as loyal as he let on. This was best proven in the Darth Vader comic by Greg Pak and Raffaele Lenco when Vader tried to retrace his past. This began to rip holes in his darkness as he was flooded by memories of his time as Anakin, but the more his hesitation in killing and desire to let particular people live took over, the more the Emperor took heed. Eventually, he tortured Vader and left him on Mustafar to try and find his strength in the Dark Side, but this would only subconsciously drive Vader further away.
There's a noticeable difference in Vader's presence in Episodes V and VI as he began to ally himself, even slightly, with Luke. While the Dark Side was still the prevailing factor in his mind, Vader was more open than ever to Luke's pull to the Light Side. Not only did this eventually work, but it was best shown in how someone who bested some of the best Jedi, including Obi-Wan, had been brutally beaten by Luke, who was not yet a master.
Darth Vader was still one of the deadliest and strongest characters in all of Star Wars. Even when he was at his weakest, he was still a formidable threat that made the entire galaxy shake with fear. However, noticing how weak he was in the Original Trilogy also showed how powerful the good was in him to take him from being a powerful creature of destruction and turning him back into the hero that audiences would later get to know better.
