The longest-tenured of those extras is Curtis Jackson (not Curtis “50 Cent” Jackson, who is a completely different guy), who played Alexandria resident Bob Miller from Season 5, Episode 12 to…sometime between the Season 8 finale and Season 9 premiere.
Yes, Bob Miller died off-screen between seasons, fans just found out.
Bob Miller never had any dialogue, but his oddly thorough wiki page details all of his appearances.
The wiki claims he made it back to Alexandria, where he died of old age, hopefully surrounded by some of his 12 grandchildren.