Plato, Aristotle, and Socrates have come up with compelling philosophies and their words continue to be studied. But I've never heard anything for Diogenes other than his weird stunts like the time he crashed Plato's lecture just to disprove what he said on humans being featherless bipeds.
Was Diogenes really a philosopher
Yes, he most definitely was. He is considered to have been one of the founders of cynicism and, by extension, a monumental influence on stoic philosophy; which was one of the most subscribed to and consequential schools of thought for much of Classical Antiquity.
Most of the information on Diogenes however, is anecdotal. No work by him survives and it is unclear if he ever wrote one to begin with. As with most historical figures, the more extreme anecdotes stand out and are more likely to be remembered by future generations.
In the case of Diogenes, the most well known include:
and of course,
Behind the theatrical stunts however, are real philosophical tenets. Diogenes, for some of his life at least, practiced exactly what he preached. This made him a different breed of philosopher; many of whom limited themselves to thought-experiments or hypotheticals.
Looking for an honest man using an oil lamp might seem as a clear sign of insanity; but it was sarcasm and social criticism at its best. Its central message (what is pure virtue but an unattainable goal?) was echoed some centuries later by a man who, arguably used a more elegant wording and less confrontational style, stated that "He that is without sin among you, let him first cast a stone."
Similarly, as Diogenes believed all of mankind to be equally worthless/ valuable ... his complete apathy and disinterest towards Alexander the Great (the absolute pinnacle of individual prestige/power in Greece at the time) was, in a way, the ultimate expression of this conviction. Had he not done so, he would have been a hypocrite; which he knew all too well.
His "bullying" of Plato, was a call to all present to be concise when presenting a definition or thought; as not doing so could undermine not only yourself but your argument as well.
Most of what we know of Diogenes comes from the Lives and Opinions of Eminent Philosophers by Diogenes Laërtius, who lived some 600 years after Diogenes himself. His influence and legacy however, while not as tangible as that of other prominent Greek philosophers, is much greater than this.