One of millions of Engineers who died millennia ago, just like the ones on LV-223.
But if David creates the Alien, the Engineer couldn't have died millenia ago with a cargo hold full of eggs. That's the question being raised: if David makes the Alien, who's in the chair?
If David makes the Alien, either there's still Engineers around, or someone else is in the pilot chair. If David re
creates the Alien, then the Engineers might be wiped out here and there's no problems.
Making up some entirely new story for what became of the jockey on LV-426 seems pointless and silly to me given that well-established framework. As does potentially sealing someone in there (or seeding the ship) only 20 years before Alien. I find that incredibly dumb.
Likewise, but it looks like that's precisely where we're headed.