Those who are interested in Philosophy should also look at Indian Philosophy. India has a rich and unbroken philosophical tradition pre-dating Greeks. This Podcast by LMU in Munich and at King's College London covers Indian Philosoply in great details.
Mine is Heraclitus, "the weeping philosopher". All we have of his writings are fragments, my favorite being:
He who hears not me but the Logos will say: All is one.
I have hope that with new archaeological discoveries, and with new technology being used to recover old, formerly unreadable documents like burnt paper which can now be read, that there will be more writings of the Pre-Socratics available for us to read in the future.
A mention of Heraclitus is not complete without also mentioning Parmenides[0]. Together, these two are the champions of their respective sides in the millennia old Being vs Becoming [1] debate. Being took a few blows at the hands of modern philosophers but I think there's plenty of room to explore the idea in the contemporary setting. The ideas we have access to now concerning relativity, quantum mechanics, space-time, and the holographic universe make it fun to explore Parmenides's idea of a static, unchanging reality that we are only able to perceive in a limited way due to our fundamental limitations as finite humans.
As a side note, I find it amusing how closely this debate parallels one of our own debates in the programming community: functional vs imperative programming.
To drag this debate down, I find it interesting that in the Marvel universe you could have put "a static, unchanging reality that we are only able to perceive in a limited way due to our fundamental limitations as finite humans" into the mouth of Doctor Doom word for word and it would fit right in ("Books of Doom" has him saying pretty much exactly that to his physics teacher as a teen), perhaps with a few minor changes ("our" to "your", probably, as the character would not want to include himself amongst mere "finite humans").
When the right writers get hold of one of the more interesting characters, there's a surprising amount of nods to philosophy to be found.
The article already mentions it but I highly recommend "The History of Western Philosophy" by Bertrand Russell, if you are interested in any type of philosophy or philosophers. It gives a good overview from the pre-Socratics up until the beginning of the 20th Century.
Recommendation: The Great Conversation, 6th edition, by Norman Melchert
Reason: The most popular history of western philosophy is Bertrand Russell's A History of Western Philosophy, which is exciting but also polemical and inaccurate. More accurate but dry and dull is Frederick Copelston's 11-volume A History of Philosophy. Anthony Kenny's recent 4-volume history, collected into one book as A New History of Western Philosophy, is both exciting and accurate, but perhaps too long (1000 pages) and technical for a first read on the history of philosophy. Melchert's textbook, The Great Conversation, is accurate but also the easiest to read, and has the clearest explanations of the important positions and debates, though of course it has its weaknesses (it spends too many pages on ancient Greek mythology but barely mentions Gottlob Frege, the father of analytic philosophy and of the philosophy of language). Melchert's history is also the only one to seriously cover the dominant mode of Anglophone philosophy done today: naturalism (what Melchert calls "physical realism"). Be sure to get the 6th edition, which has major improvements over the 5th edition.
"Kirk and Raven" is the standard textbook in English. Gives and discusses the principal testimonia and fragments in the original Greek (or Latin) with English translations.
[1] http://historyofphilosophy.net/india