Darth Vader

Darth Vader was an alias of Marty McFly during his first temporal incursion into the year 1955. 'Vader' was supposedly from the planet Vulcan. (Back to the Future)

History
As a result of this temporal incursion, the younger version of Lorraine Baines (the future Mrs. McFly), fell in love with her time travelling son instead of George, her future husband. After a number of attempts to try and convince the painfully shy George to ask Lorainne to the Enchantment Under the Sea dance had failed, Marty decided that more drastic measures were required.

George had emphatically declared that there was no way on Earth he'd ask Lorraine to the dance, so Marty came up with a way around that particular arguement. Donning his radiation proof outergarment and hood, Marty snuck into George McFly's bedroom at some dark hour of the night. Utilizing a Sony Walkman, a hair dryer, and cholroform, Marty prepared to make some fairly compelling arguement for George to ask Lorraine to the dance (see quotes).(Back to the Future)

The incident affected George to a point that his first novel, A Match Made in Space was based on this particular incident. When published in 1985, George had to change the name of the extraterrestrial in order to prevent copyright infringement with Star Wars creator George Lucas.

George would not connect the dots about Darth Vader being a his time travelling son until the year 1991 when he visited Marty at the Institute of Future Technology. He, however, admitted that there was something oddly familiar about this 'Darth Vader' character from Star Wars when he watched the movie with Lorraine in 1977. This story, combined with that of a stranded Voyager away team, made him start furiously taking down notes for his next book. When George asked Tom Paris who the identity of Darth Vader should be, Tom facetiously said, "Tuvok of Vulcan..." (Star Trek: Voyager - Dark Realm)

Quotes
Marty: ''"What made you change your mind, George?" ''

George: "Last night, Darth Vader came down from planet Vulcan, and he told me that if I didn't take Lorraine to the dance, he'd melt my brain."

Marty: "Yeah, well, let's keep this brain melting stuff to ourselves, okay?"

George: "Oh, yeah. Yeah."

— Discussing why George is going through with Marty's plan despite previous denial