E.T. the Extra-Terrestrial/WMG

ET was the first alien ambassador to Earth.
Never forgetting his "connection" with the stars, Elliot eventually became an astronaut. His great-grandson will eventually be the first man on Mars, and his family will carry on a proud spacefaring tradition.

Thousands of years later, with humanity dispersed to other planets in the galaxy, a distant descendant of his will briefly consider joining the space fleet of the central galactic military, until a certain moisture farmer from an obscure desert planet will convince him to take up the rebels' cause...

PS: Elliot's Disappeared dad was a somewhat libertine archaeologist who loved treasure-hunting a bit more than a quiet suburban life.

Okay, now we just need the mandatory guesses about Haruhi Suzumiya, Neon Genesis Evangelion and Time Lords.
 * People keep getting the impression that Star Wars takes place in the future. The "Long time ago in a galaxy far far away" most likely means that it's set millions of years before our planet was created and civilized. Many galaxies could have humans and humanoid lifeforms with technology that may seem advanced but are older than ours.
 * The thing about humans in Star Wars is a bit debatable. Lucas and co. have always been deliberately vague about the origin of humans in the Star Wars universe, but it's been established that, while humans are the dominant species on many worlds in the galaxy (Alderaan, Corellia and Coruscant, to name a few), they aren't indigenous to any of those planets--they're colonists who arrived from some unknown planet thousands of years in the past. Theories abound, but it's natural to assume that said planet was Earth.
 * And there was a planned (but unreleased) novel called Star Wars: Alien Exodus that would have established that humans wound up in the galaxy after fleeing Earth and traveling through a time warp. Some fans still consider this explanation Canon. If this is true, it would mean that the humans are from Earth's future, even if the events of the series take place in the past. The meeting with E.T. could have inspired humans to make the trip into space that would end with them going through the time warp.
 * This is actually somewhat Canon. In The Phantom Menace, George Lucas purposely included a shot of a group of aliens in the Galactic Senate that look like E.T. as a Shout-Out to Spielberg. It's since been established that they come from a planet called "Brodo Asogi" (one of the names given to E.T.'s home planet in the spin-off novel E.T.: The Book of the Green Planet), and that their ambassador to the Senate is named "Grebleips". An entry on the Star Wars website "HoloNet News" also mentions that Grebleips was involved in funding an exploratory expedition outside the Star Wars Galaxy, but the results of it are unknown...


 * Wild Mass Guessing

Elliot's Father
Instead of a certain archeologist suggested in the WMG above, Elliot's father is actually Mutt Williams aka Henry Jones III.
 * This is actually much more likely. If he's 10 years old, Elliot would have been born around 1972, at which point Indy would be 73 years old (he was canonically born in 1899) and pushing 80 when Gertie came around. Even for Indiana Jones that's a bit hard to believe. Mutt, assuming he was conceived during or shortly after the events of Raiders, would likely have been born in early 1937, which would make him a much more reasonable 35 for Elliot's birth.