Williams was a friend of Fisher and was visiting the set, and supposedly was allowed to be an extra while there.

They are credited as Echo Base trooper “Jesse Allashane” who is not named in the actual movie and I’m not even sure are notably onscreen at any point.

When the Hoth expansion was released for the Star Wars Customisable Card Game in the 90s, the character was created using a production photo supposedly of Williams as a Hoth Rebel soldier extra.

That said, Arve Juritzen also claims to be the person in the photo used for that card. So the only actual identifiable images of Williams in Empire is the photo OP has posted and a few other production stills taken. I don’t think anyone has ever actually spotted him in the film itself (possibly didn’t make the cut).

Reminds me of Patrick Muldoon in Starship Troopers.