Darth Vader is a fictional male Human in the Star Wars series. His allegiance / loyalty is to The Galactic Empire. Darth Vader is the main antagonist in the original films. On screen, Darth Vader is played by David Prowse, a British bodybuilder who was also known at the time as the Green-X (as in Cross) man owing to his appearance in road safety campaigns at the time. As David's voice didn't fit, his character was voiced-over by James Earl Jones. Darth signifies that the character is a dark lord of the Sith. Other Darths in the films are Darth Maul and Darth Sidious, the latter being the alternate name for Palpatine.
Darth was once a human from Tatooine who got corrupted to the Dark Side of the Force by Senator Palpatine and now Emperor Palpatine. He wears a mask as he was heavily disfigured in a fight on the lava planet of Mustafar at the end of Star Wars III - Revenge of the Sith.
Before turning, he was known as Anakin Skywalker born to a slave Shmi Skywalker on the planet of Tatooine. He is a father but this not revealed until Darth Vader fights Luke Skywalker in Cloud City, Bespin.
In the film he is tasked by the Emperor Palpatine with finding the stolen plans of the Death Star, an artificial planet. He does this by hijacking the Tantive IV ambassador ship and kidnapping Princess Leia Organa from the planet Alderaan. Darth Vader takes Princess Leia back to the Death Star for interrogation. Throughout the film, there is no indication that Princess Leia is his daughter, that doesn't happen until the third and final film.
When the Rebel Alliance attack the Death Star, Darth Vader commands a TIE Fighter to assist in the defence of the artificial moon. Vader's fighter is hit which is then shot off into space thus protecting him from being destroyed.
Darth Vader leads the hunt for the Rebel Alliance from onboard the Super Star Destroyer Executor which if you thought that the Star Destroyers was massive, the Executor is five times if not more as big. Darth takes the Imperial fleet to the Ice planet Hoth after one of its probes were destroyed on the surface by Han Solo. After the initial attack has been completed, Darth lands on the planet to venture inside the remnants of the Rebel base but by the time of landing, everyone has by that time escaped.
Darth Vader returns to the Executor and chases the Millennium Falcon from it leaving Hoth through an asteroid belt only to loose it when Han Solo hides the Falcon on the side of a star destroyer. Vader takes the fleet to Bespin to make a deal with Lando Calrissian, Han Solo's old friend. Darth only wants Luke Skywalker and by capturing Han Solo, Princess Leia and the rest of the Falcon crew, he hopes he can lure Luke to City to capture him. The plan works and Luke and Darth Vader duel. In one of the most memorable twists in cinematic history, Darth reveals to Luke, he is Luke's father. After defeating Luke, Darth Vader walks off.
Darth Vader oversees the arrival of the Emperor on the nearly finished second Death Star. For the first half of the film, he is noted for his absence a most of the action takes place on the desert planet of Tatooine where the Rebels take to rescue Han Solo from the gangster Jabba, the Hutt.
When Darth Vader finally appears again, he is sent to a Star Destroyer to oversee the destruction of the Rebel fleet that has appeared. Darth visits the surface of the Moon of Endor to meet Luke Skywalker who has turned himself into the Empire. Darth takes his son to the Emperor who tries to persuade him to turn to the Dark Side but Luke manages to resist. The Emperor wants Luke to duel with Darth Vader but that only happens when Darth Vader discovers hat Luke has a sister, Anakins daughter, the Princess Leia Organa.
Luke Skywalker manages to win the fight but declines to kill hs father. When the Emperor starts inflicting pain on Luke, Darths fatherly instinct comes to the fore and saves his son by throwing the Emperor down a shaft thus killing him.
Badly injured and is dying, Darth gets to see his son one last time before he dies. Luke takes the body and leaves the crumbling Death Star before it explodes. Luke cremates his father before joining the others celebrating the end of the Empire.
There was never any doubt that one of the most iconic characters of all time was ever going to appear in the film albeit a small part. Darth Vader has a guest role within the Star Wars - Rogue One film. Even though Darth Vader lost his limbs and became heavily burnt on the planet, he made Mustafar his home where he undergoes medical cleaning in his castle. When we first see him, he is in a cloudy tube badly burnt and then being put into his suit. He is protected by Imperial Red Guard, the kind that you saw guarding Emperor Palpatine in Star Wars VI - Return of the Jedi.
When Director Krennic comes to visit Darth Vader, they discuss the operation of the Death Star and then Darth force strangles the Director as a warning to not get too ambitious.
Once the Death Star plans have been stolen, Darth Vader is despatched to recover them from the Rebels who have them aboard their Tantive IV space ship containing Princess Leia. Darth Vader is seen wielding his lightsaber, the only time a lightsaber is seen in the film as he fights off the Rebel soldiers fighting to protect their cargo plans.
Ben Solo, the grandson of Anakin Skywalker tries to emulate what his father was. Kylo Ren wears a mask for the majority of the Force Awakens. When he chastised by Supreme Emperor Snoke, Kylo Ren destroyed his mask in a fit of rage and from that point on, no longer wears a mask. There is no direct reference to Darth Vader in the film, no visuals, no ghost.