"Zoning" Out, Episode VIII: Dust
Living forever isn't the best revenge

"LONG LIVE WALTER JAMESON" - March 18, 1960
Pursuit of immortality is a common trope in science-fiction, generally wrapped in a a lesson about how all things must perish at some point, and endless life is not all it's cracked up to be. "Long Live Walter Jameson" is one of several episodes of The Twilight Zone that covered the subject, and is arguably the best one to tackle it. Penned by Charles Beaumont, the season one episode possesses little to no sentiment, but instead is a haunting and ultimately horrifying 30 minutes - the kind of terror that may or may not have caused a young kid watching this episode during a Chicago Cubs rain delay to be mortified by the show for many, many years.
(I got better.)
Walter Jameson is a well-liked professor, known for telling tales of history to such minute detail that you might excuse the thought that he almost seems to have lived it, rather than simply researched it. When the episode begins, he is telling a story of Civil War soldier Hugh Skelton, directly from the man's journal. Listening to the story is fellow professor Sam Kittridge, who has additional interest in Jameson's performance, as his daughter Susanna is his betrothed. The two have a warm, but awkward relationship due to that, and later in the evening when Walter pays a visit, Sam and Walter argue over whether or not Susanna is going to be a housewife or use the Doctoral degree she is working on in the workforce.
Sam then brings up another thing that is bothering him - the men have known each other for a decade or so, but while Sam has aged and is growing old, Walter has not, and looks the exact same as the day they met. Walter tries to deflect with excuses of how people age differently, but this is only met with more suspicion. Sam then explains that he went through and found a photo of Hugh Skelton, and, well, it looks exactly like our pal Walter here. Sam tries to pass it off as a relative, but Jameson tells the truth - it is him, and with the dam open, he explains to Sam that he is thousands of years old, "blessed" with immortality by a nameless alchemist who had vanished by the time Walter awoke from the experiment.

Walter explains that he is tired of being alive, tired of having to leave people behind and watch them grow old while he doesn't, and does want to die, but is too cowardly to end his life. He is immortal, sure, but just from natural causes - he can't survive a gunshot or being decapitated or thrown into an industrial shredder or something like that. He has a gun to perform the ritual, but can't bring himself to do it. Sam then suddenly realizes that his own daughter is set to marry a man who otherwise cannot die, and the cycle will repeat itself with her, and Walter will disappear without a trace before he is found out. Knowing Susanna will think her father mad, Walter talks her into eloping tonight and she agrees. He returns to his home across the street to prepare until... oh no, disaster!
A voice from his past calls out, using a different name, that of Tom Bowen. He doesn't seem to recognize her, possibly in truth, but likely to deflect her aggression and paint her as crazy. It's a former spouse, who herself had been left behind when she aged and he did not. He continually tries to deny this, naturally, but she is not deterred. Clearly Walter did not move far enough away from where he left her. Ultimately, she sees the gun that Jameson referenced in his discussion with Sam - Chekhov's Gun exists in many dimensions - and as Sam heads over to try and talk Walter out of running off with his daughter, he hears the gunshot.

Sam arrives too late, as he soon discovers. Walter has been shot, and his life is about to be forfeit. After recovering from the shock, he is at peace with it, knowing it's finally going to be over for him. What happens after is where the horror truly arrives, as Walter rapidly ages to match his actual lifespan, until he becomes what you see above. Susanna arrives later, and Sam has to cover what happened by explaining that what she sees is just... dust. Then they took the concept and reused it for another creepy episode in season five with the exact opposite moral, which is fun.
As you might expect, this is a haunting episode about a man who has lived a long time, and has reached a point that he wishes it could end, but also has no ability to call up Cadwallader for an easy escape. His foil, Sam Kittridge, is afraid of death and anxious to be aging and wishes Walter could tell him the secret, but he cannot. While Walter is a villain in the story as someone who knows he is harming people by abandoning them over the years, he's also portrayed as sympathetic because he knows he is doing wrong but is scared to do what's right to end the charade. Kevin McCarthy is an actor I mostly knew as the evil station manager in "UHF" because I had mentally blocked this episode, so I immediately assumed he was a bad guy, but he really wasn't. He was just a dude blessed with something he should never have been given.
"Long Live Walter Jameson" is one of the many strong season one episodes that doesn't quite get all the recognition it deserves, due to lacking a standard shock twist that can be used as shorthand for the episode. Once we heard he was functionally immortal, and had a gun lying around we knew something was going to happen, we just didn't know how it would happen. Instead, the unease of the reveal and the uncomfortable dialog creates tension and the kind of otherworldliness that makes Twilight Zone tick.