Don't mean to be a stickler but a majority of definitions for this man appear to be gravely erroneous. He was a rationalist of Portuguese Jewish descent with a nascent philosophical background in the same vein as Descartes, Democritus and Epicurus. Stoicism if you will.
He was issued a Cherem and ostracized from the Jewish community in the Netherlands for his Theologico-Political Treatise which suggested that sacred works such as the bible be examined critically and rationally as opposed to arbitrarily treating such works as infallible works of a supreme being with a specific purpose for humans. Spent the rest of his life working as a lens grinder. What better way for the man who supposedly moved Einstein to bad poetry to live? Building tools to help us see the world better, and trying to understand the world? Wow. He dies in his mid-forties. His philosophy revolves around a deterministic monism.
Simply put, Spinoza advanced the proposition that there is only one eternal substance, nothing exists outside of it and this substance is God and everything including our thoughts are all in God. Deus sive Natura.
Last point of note: He spent a great deal of time in his work ethics, which was presented in geometric order, refuting the idea of an anthropomorphic deity. By the standards of the Abrahamic religions and probably all religions, this view would be atheistic, so be careful.
Fun Facts: Spinoza posited that a life devoted trying to understand the universe and everything in it and ignoring ephemeral goods like paris hilton and the new iphone was the true path to immortaility. He called this filling the mind, which is a mode of the attribute of thought (God has infinite attributes) with adequate ideas.
His ideas were considered heretical so he was extremely careful. People were being slaughtered for much less in his time and still are. "Sub Rosa" was an emblem on a ring he allegedly wore.
Last factoid: He solved Descartes notorious mind/body problem by positing that mind and body were two modes of expression of the same substance, God, under two distinct attributes: Thought and Extension.
Rationalist philosopher dude who lived a long time ago.more...
He basically said that substance is god, or nature, and that every existing thing is one. That kinda made Christian Europe mad and they actually started using the word "Spinozist" as almost a swear word for "atheist".
Then there was this huge intellectual controversy when Jacobi and Mendelssohn were both writing a book about Lessing, who had just died, and they started exchanging letters about it and things got kinda heated when Jacobi took things a little too seriously and competed to have his book printed first. Mendelssohn didn't get as aggresive as Jacobi, but the poor dude ended up dead when he caught a cold trying to send in his manuscript.
Anyway, the reason why this caused so much controversy was because Jacobi claimed that Lessing admitted to being a spinozist and Mendelssohn was friends with Lessing so everyone was like omg no way cause Mendelssohn was a leader of the Berlin Enlightenment and the starter of modern Judaism and being called an atheist or pantheist wasn't exactly a good thing back then.
Long story short, Jacobi's book got printed, in which he actually criticized Spinoza saying that yeah, Spinoza may be right in his ideas but reason leads to atheism and denial of free will so we should have faith. Or something like that. Bu interestingly enough, this criticism restarted an interest in Spinoza. And here we are today, still talking about the dude.
The sexiest philosopher to have ever lived. That fact was confirmed by the Romanian Sex God. His work is not meant for light reading, but is possibly good while drunk.
"Spinoza makes me think happy thoughts.... about your mother!"
An atheist Dutch philosopher of 17th century who largely inspired Karl Marx.
As Spinoza puts it: the belief in our liberty is only the flaw of the knowledge we have of our limitations and determinations.