I have a great amount of respect for the near-forgotten figure Max Stirner. His ill-famed "The Ego and His Own" is probably the most radical, thought provoking and challenging writting that I have ever read. Not only did Stirner explicitly take an egoist position, question the very foundation of morality and critisize modern liberal secularism as not going far enough numerous decades before Neitzsche (and arguably manage to be even more radical than Neitzsche), but he did this as what many think is meant to be the logical completion of Hegel's project and during the same period as and loosely being associated through academia to Karl Marx and Engels.
The "young Hegelians" or "left-hegelians" such as Ludwig Feurbach and Karl Marx all had interacted with Stirner on a personal level in Academia prior to the release of "The Ego and His Own", and from their own perspectives they were trying to surpass Hegel. These young Hegelians came to take an explicitly atheist position, hence aschewing all of the overtly religious elements from the Hegelian project and shifting the emphasis more towards man or humanity. The end result tended towards some kind of secular humanism, and eventually communism as proposed by Marx and Engels (although the communism of Engels was arguably less collectivistic than that of Marx).
Stirner was a student of Hegel himself and passively participated in some of the interactions that took place among the left-hegelians. When he formally released "The Ego and His Own" it greatly shocked many of his collegues, since it took the Hegelian project in an entirely different direction and quite explicitly critisized the left-hegelians as only replacing the old godhead with a new one. Stirner did not critisize the left-hegelians on the grounds of their atheism, but on the grounds that they still cling to concepts that function in the same way as religion. From Stirner's perspective, they had not followed the logical progression far enough. The modern secular liberal had destroyed the basis for an incorporeal god but then proceeded to divinize earthly things and "humanity" in the abstract. In short, the cloak of power had only been secularized, not eliminated. The higher cause of the god had been functionally replaced with the higher cause of the state, the nation, humanity and all sorts of abstract concepts.
This realization of Stirner's and the period during which he realized it is not a trivial matter. Stirner's criticism applies about just as much to contemporary secularism now as it did when he wrote about it. Furthermore, the implications of what Stirner realized is more far reaching than a criticism of secular humanism, it has immense epistemological implications. Stirner effectively denied transcendentalism and rationalism long before anyone classified as a post-modernist did and he reached the conclusion of what by the very least is a strong nominalism using an egoist framework. Stirner had technically surpassed the entire enlightenment project by proclaiming that we should not be ruled by concepts. The enlightenment and secular humanist emphasis on the mind, from his perspective, was just as filled with "spooks" as religion. This is really just an extension on the phenomenology of mind.
While Stirner has been influential in one way or another on many anarchists (ranging from Benjamin Tucker to Emma Goldman) due to his rejection of the state and some of the aspects or implications of his egoism, he also rejected "morality", at least "morality with a big M", and critisized anarchists such as Proudhon for still clinging to morality. To be sure, Stirner seems to put the anarchist on a somewhat higher level because the anarchist doesn't accept the arbitrary authority of the law while the typical secular humanity or liberal still does, but he nonetheless critisized anarchism on the grounds that it still ultimately clung to a human-based morality. This is the point at which I personally start to struggle with Stirner, for while my own views on secular humanism and modern liberalism mirror his in many ways and I'm intrigued by the directions he took the phenomenology of mind, I am an ethical anarchist. That being said, the extent to which Stirner may really be an ethical nihilist is debatable.
Stirner also rejected the traditional notion of revolution, although this was actually picked up and adopted by many individualist anarchists. Certainly not all anarchists believe in violent revolution, revolution for its own sake or at least revolution in the same of a mere change of the seat of power (state-democratic revolution, if you will). So it's questionable wether this criticism should be interpreted to apply to all anarchists per se or wether the criticism is limited to anarchists. There are plenty of people who advocate violent and state-democratic revolutions who are not anarchists and most certainly only wish to change the seat of power, and there are plenty of anarchists who take either a pacifist stance or are generally not comfortable with the traditional method of revolution. If anything, Stirner's criticism could be applied as an anarchist criticism of political libertarianism.
If Proudhon is considered the first formal anarchist, Stirner is definitely the first formal egoist. To be sure, due to the implications of Stirner's phenomenology, Stirner was not an ethical egoist along the lines of Ayn Rand. There are different types of egoism, ranging from nihilist egoism to psychological egoism to ethical egoism. Nonetheless, it seems undoubtable that Stirner has been indispensibly influential on egoism in general, and he must have at least indirectly influenced Neitszche and Ayn Rand in one way or another. Whether or not Neitszche ever read Stirner (and even if he plagiarized him) is a controversy that hasn't been given a rest and has often been pushed under a rug, but I think it's rather undeniable given the historical period and academic connections that Neitszche must have read Stirner's "The Ego and His Own" at once point or another, and some studies have collected some fairly compelling evidence that he must have.
Stirner is not an easy person to classify. While he appears to very strongly oppose communism, democracy and humanism, there is no evidence to indicate that he was necessarily any more supportive of capitalism, conservatism and traditionalism. A knee-jerk response to Stirner from your average secular liberal may be to misunderstand him in such a way, but this is mostly due to cultural cliches and misunderstandings about egoism and individualism. But if anything, Stirner has surpassed all of these things from an egoist framework and as a consequence of his phenomeology. It is also possible for Stirner to be misunderstood as presenting a religious argument against atheism, but this kind of misunderstanding is only an affirmation of Stirner's criticisms of secular humanism.
The reason why Stirner has been pushed under the rug as a philosopher and figure in general, beyond the mere radicalness of his ideas by itself, largely has to do with Marx's own attempts to counter Stirner and all Marxist and post-marxist scholars more or less accepting Marx's line on Stirner. Marx obviously saw Stirner as a threat to his own project, and effectively denounced Stirner as a "petty burgouesie individualist". Very little criticism was directly aimed at Stirner's ideas, it was more of an emotional or knee-jerk reaction. The philosophical community in large part was either silent or dismissive of "The Ego and His Own". It was clearly far too radical for its time and even our time. But it's a shame that the reaction to Stirner has been to marginalize and ignore him, relegating him to a tiny little footnote in history. I highly suggest that anyone, anarchist or otherwise, read "The Ego and His Own" to challenge themselves and perhaps seek inspiration. Stirner most definitely is not irrelevant, and perhaps will become increasingly more relevant over time.