I love roguelikes and ADOM is the one that got me into them way back in 1997. I have played it off an on since then, probably logging about 200 hours, most of it in my teenage years. I want to be open though with the fact that I have never beaten it. I have not even come close, I rarely get to the caverns of chaos even, which most people who know the game well would probably hesitate to even call the mid game.
However, I have read a lot about the advanced parts of the game and I totally love it. The Trident of the Red Rooster is one of those parts. The Trident is the ultimate item of the game. It has a staggering list of prerequisites, things that are obscure and difficult and that must be planned for from the very beginning of the game.
You could actually beat the game several times over and probably not know of the trident. But if you look close enough (or read spoilers) you will find that it is totally baked into the lore of the Drakalar Chain. And that is part of what I love about Adom, it has bits of tsatic content like the Trident mingled into the randomly generated content. I think it adds a huge amount of depth and familiarity to the game, and helps to create a real living breathing world instead of just some dungeon dive.