The safest general characterization of the European philosophical tradition is that it consists of a series of footnotes to Plato. ~A.N. Whitehead

Christianity ... Platonism for the masses. ~F.N.

Plato (428? - 348? BCE)

nihilistic position — only the abstract (i.e. super-sensible/super-natural re: 'The Form of the Good' (i.e. universals, the absolute)) is significant and the sensible (empirical)/natural is comparatively insignificant.

contribution — Platonic Realism + 'Socratic method' & dialectics + early christian (pre-thomistic) theology ...

H.P. Lovecraft (1890-1937)

nihilistic position — 'cosmic insignificance' of human beings, our values, actions, and human civilization ...

contribution — (literary) Cosmicism + stories of 'cosmic horror' (NB: I prefer Thomas Ligotti (b. 1953), esp. The Conspiracy Against The Human Race)

Ray Brassier (b. 1965)

nihilistic position — philosophy is "the organon of extinction", that thinking correlates with non-being (its own a priori extinction, or "anterior posteriority" ... "necessary contingency" (Meillassoux)) rather than with being, pushing the (Enlightenment's) 'disenchantment of the world' to its (onto)logical conclusion ...

contribution — Transcendental Nihilism (re: Nihil Unbound: Extinction and Enlightenment)

H.P. Lovecraft (1890-1937) — 180 Proof

I've never thought of him as a philosopher, but I suppose he was in a way. Cthulhu and Great Old Ones diminish human existence.

What about the anti-nihilists, or rather, the reverse-nihilists? "Out of nothing came I." Sort of reverse-engineering nihilism. Transcoping decadence of matter, refurcating the third law of thermodynamics. Explaining abiogenesis so that a fundamentalist preacher in the Deep South can be converted to preach it to his or her congregation. The Grand Remaking of America. The Great Restart, or Unstart. Uncreating the sun. Inventing the wheel, backward. Extinguishing fire, getting back up on the tree.

Arthur Schopenhauer - 19th century German Idealist tradition-
Main philosophy: Existence is Will- a striving force/principle, but manifested as phenomenal existence (Will mediated through the fourfold root of the Principle of Sufficient Reason). This manifested/mediated version of Will causes being to be bifurcated as if it was subject/object and causes great pain for the individual animal/being that strives but without end or satisfaction. Life is equated then with kind of dissatisfaction/suffering discussed in Buddhism and Eastern philosophies. It was best never to have been born if looked at in foresight from parent /hindsight from already being born. Once born, art, aesthetic experience, compassion for fellow suffering beings, and ascetic denial of the very Will at the core of being are avenues one can try, but often fail to achieve.

David Benatar- Modern ethicist at University of South Africa Cape Town.
Main philosophy: There is an asymmetry between the absence of good and bad. Pleasures are good and pains are bad when existing. Absence of pain is good, even if people don't exist to know it. Absence of pleasure is not bad (or good), but neutral unless someone already exists to be deprived of that good. Therefore no one is obligated to bring about people who have benefits, but are obligated to prevent people who have pain.

Nihilism is a broad category, and these two arent necesseraily nihilists unless philosophical pessemism counts as a form of existential nihilism, which is debatable.

For a proper understanding of what nihilism is, and what nihilists are, you must watch The Big Lebowski.

Although I'm leaning towards nihilism because skepticism, even the most radical ones, resonates with me, I have this suspicion that nihilism, in certain respects, makes the mistake of looking for objectivity and rationality in areas that are, by their very nature, subjective and arbitrary. For instance "...human principles and social institutions..." bears the mark of our tastes rather than reason and that's perfectly fine by me. To seek objectivity/rationality in what's fundamentally neither is being a bit too unreasonable.

According to Nietzsche, Schopenhauer was an atheistic nihilist because he advocated for the Denial, rather than for the Affirmation, of the Will to Live. Despite relinquishing belief in the purported "self-contradictory" notion of God, he, nevertheless, continued to extol and subscribe to the God-derived Judeo-Christian system of values whose ultimate 'salvific" goal for all humanity was achievement of the ideal nirvanic state of Nothingness.

One could make a strong argument that Schopenhauer contributed significantly to the development of Nietzsche's philosophical thinking. Like Schopenhauer, Nietzsche was also an atheist but, in several crucial ways, Nietzsche's thought was the exact opposite of Schopenhauer's. For example, Nietzsche advocated, instead, for a deliberate human control over and enhancement of the Will to Live, referring to it as the Will to Power and, instead, he rejected the Judeo-Christian system of values, since its God and purpose was "dead." And, most importantly, he advocated for the creation of a new system of values, a neo-aristocratic system of values, grounded in the Will to Power, which would be a trans-valuation of the prevailing Judeo-Christian "herd morality" system of values. And, also, he advocated for the free creation of a new, universal, secular goal for humanity to strive toward and to realize.