Does Supernatural pave Dean Winchester's road toward killing Death as early as season 1? Hunting monsters is hardly the most conventional career path, but just like any other profession, newbies must work their way up the paranormal promotion ladder. This is certainly true for Supernatural's Sam and Dean Winchester, who begin in season 1 fighting ghosts, wendigos and CGI bugs, and finish season 15 taking down God himself, not to mention many of the Good Lord's troublesome family members.
That progression doesn't happen overnight, however, and Supernatural gradually pits Sam and Dean against bigger and more renowned opponents. One of the earliest occasions where the Winchester brothers kill something truly biblical comes in Supernatural season 10. Dean Winchester meets Death (the original Julian Richings incarnation) in a Mexican restaurant, hoping the Grim Reaper can scythe him to end the Mark of Cain's increasingly tight grip. Instead, Death decides Sam should be the one to perish, and hands Dean his scythe, allowing one brother to kill the other. Dean grapples with his inner turmoil, before ultimately deciding neither of Supernatural's Winchester brothers should die, and turning Death's own blade against him.
Death's death easily ranks among Supernatural's most shocking moments. The Grim Reaper was a primordial entity destined to reap God at the end of time. Audiences weren't even sure whether Death could be killed until Dean sliced through him like a soggy apple pie. As surprising as Dean killing Death might've been in Supernatural season 10, the moment had long been foreshadowed, even as far back as the CW show's debut season. In 2006 episode "Faith," the Winchester brothers come up against Roy Le Grange, who is unknowingly healing the incurable by using a Reaper to trade one life for another. Discussing how to approach their latest spooky dilemma, Sam refuses to kill Roy on moral grounds, whereas Dean ominously utters the line, "We can't kill Death." Nine seasons later, Supernatural brings this "kill Death" line full circle when Dean Winchester does exactly that - a serendipitous moment paying off a decade-old piece of dialogue spoken by Dean himself.
When Dean tells his brother, "We can't kill Death" in Supernatural season 1, he's saying two hunters wielding machetes and copious amounts of salt can't hang with an entity of such high arcane stature. Roy's Reaper is working on behalf of Death himself, and if the Winchester brothers could only take out the man in charge, they'd no longer have a suspect Nebraskan faith healer problem. But Dean's line also betrays how the older (and, let's be honest, more trigger-happy) Winchester brother was at least considering the prospect of killing Death as early as season 1 - he just couldn't fathom how that would actually happen. This early into Supernatural's timeline, the Winchesters had no way of finding Death, no weapon that could kill him, and no means of catching the Grim Reaper off guard long enough to strike a blow.
It's very unlikely Supernatural intended Dean's "we can't kill Death" line to directly set up a future moment where Jensen Ackles' character actually does kill Death. Supernatural's creator, Eric Kripke, has previously revealed his lack of long-term plans for the show, especially beyond season 5. Nevertheless, the ironic reversal of Dean's attitude toward Death looks poetic in hindsight - a happy (albeit rather morbid) accident.
Supernatural's Dean/Death foreshadowing also highlights just how drastically the Winchester brothers evolved during their hunting exploits. In season 1, the notion of killing Death was immediately written off as the stuff of fantasy. Come Supernatural season 10, Sam and Dean were not only on first-name terms with Death, but found themselves in a position to end him.