In many fantasy settings, Elves come in a large number of varieties (a tendency often lampooned as "an elf for every occasion"). One of the more common varieties are High Elves, which are usually the setting's "default" elven race. In most(but by no means all) cases, they will be pretentious assholes who rest on the laurels of their civilization that was probably once the greatest in the world, ignoring the fact that the round-ears are catching up or have exceeded them.
Lord of the Rings
The central elves of the book series are known as the High Elves and also the Eldar, hence where Games Workshop got their own names for their own elves in fantasy and elves in space respectively. They are responsible for impacting on the personification of High Elves in many fantasy settings afterwards. In the context of the series, the label "High Elves" is primarily used to describe the Noldor, one of the three ethnic groups of elves and the most advanced in terms of craftsmanship. They are "high" in comparison to the other elves of Middle Earth, with the Sindar elves having their own robust civilization but not quite as advanced as the Noldor, and the Silvan elves, who basically are the archetype for Wood Elves. They're effectively immortal (in that they are ageless and can't die from disease or old age), unearthly beautiful and a wicked shot with a bow and a deadly strike with a sword. At first the Noldor had intentions of being the dominant power in Middle-Earth, but after their ass-whooping at the hands of Morgoth, they've been gradually migrating back to the Undying Lands, with increasingly less contact with the other nations of Middle-Earth, to the point that their large kingdoms have disappeared into tiny, hard to enter enclaves.
See High Elves (Warhammer) for further details.
These elves took the idea of a dying race from Tolkien and took it a step further, adding the grimdark of the setting to concept. Now the Warhammer High Elves have no safe place to retreat to, their birth rate is declining and their people dying and their culture is under constant threat of destruction. So yes pretty grimdark indeed. But unlike Tolkien's elves, they're not at all passive about it, and this raw stoicism in the face of what seems to be inevitable destruction makes them Awesome.