Rogue, Nethack, Angband, and others were ASCII-based dungeon crawlers prevalent in the late 1980's. And they were difficult. I played them all, but only ever won Angband, and that only twice. Among other things, the difficulty arose from the fact that levels were randomly generated and that death was permanent. Put simply, the only mode in those games was hardcore.
Diablo (1 and 2) came from the same tradition as the Roguelikes -- in fact there was some early controversy on the roguelike forums that the core code for Diablo 1 had been illegally taken from the free-but-not-to-be-used-for-commercial-purposes Angband code. But really it would have been more surprising if no-one had suggested that possibility, so who knows?
Now I didn't play Diablo 1 enough to remember much about it, but Diablo 2 did have hardcore mode, and death was permanent for characters created in that mode. Hardcore mode in Diablo 2 was easier than in the earlier roguelikes because the random factor was lessened. In other words, as long as you had played enough to know exactly where all the dangerous points were, you could then play hardcore mode successfully by religiously following a fairly small set of rules of caution. There were similar rules of caution in Angband (e.g. don't descend to level x before you have stats y) but no matter how cautious you were, the random factor could always surprise you and force you to start over.
Nonetheless, I never beat Diablo 2 (defeated Hell Baal) in hardcore mode. If I recall correctly, the furthest I got was Nightmare Ancients and I think I could have continued, but the extreme patience required finally wore me down. For those unfamiliar, Diablo 2 had you play through content in 3 modes: Normal, Nightmare, and Hell, with each mode having the same essential content, but with successively more difficult encounters. The Ancients were one such encounter, and was particularly difficult to get pass if you were not properly geared. So "Nightmare Ancients" refers to the Ancients encounter in Nightmare mode, and I stopped there because I knew I was not geared up enough to succeed. What I would have had to do is to grind previous areas until better equipment dropped, and then I could have confidently continued.
And then came the mmos.
World of Warcraft took away any sense of hardcore mode. Sure, you can play with the intent of never dying, but death has no real consequence (other than as a statistic) so there seems to be little point in trying. The Lord of the Rings Online does have a mini-hardcore mode in that you receive the Undying title if you survie to level 20 without dying. But Turbine has stated that they would never offer titles for hardcore play after level 20 because it would encourage people to avoid grouping -- or really to avoid doing anything interesting at all.
While I agree that it would be a terrible idea to extend Lotro's hardcore mode beyond level 20, I still really enjoy going for the Undying title. Its not a title I actually wear -- its rather common and there are more interesting ones to be had -- but I do thourougly enjoy playing with the knowledge that if I did, something permanent is lost, even if it is only a title.
Don't get me wrong, I only enjoy hardcore mode in games to a very limited extent. Even back in the day when playing roguelikes I would frequently cheat and make copies of my saved game so that I wouldn't have to start all the way over on death. Indeed, it's only because of my frequent cheating that I was able to become good enough at the lower levels to eventually win the game without cheating. For some, cheating such as that would have ruined the excitement completely, but death still meant something because I knew full well if any particular game counted or not. After a first death, I wasn't really playing any more, I was just practicing.
In Diablo 2, my hardcore experiences were also limited. I played 90% of the time in easy mode, but I suppose in my head my goal was always to win in hardcore mode, so the easy mode playing was again just practice.
So, I'm not a true hardcore player, but I really miss the excitement that limited hardcore play provides. In the modern mmo, there are occasional glimpses of this excitement. There are times when one must fight their way through a vast underground complex, or up through the ruins of some abandoned city where, if one dies, one must start all the way back at the beginning knowing that all the mobs will have respawned and that many hours will have been lost. This is the sort of thing that players will inevitably complain about and point to as being annoying or even stupid. But I know in my heart of hearts that those places are really the only surviving bastion of hardcore play, and that they must be preserved at all costs.