I am afraid that there's is a bit of chronological bias going on here.  Let me explain my (lone) vote for Heron of Alexandria (also spelled “Hero”).  I saw a show on him on the History Channel and was simply amazed at the man's genius.  He built these boxes which served the ancient Greek/Roman purpose of our modern television.  The boxes contained cut out scenes and characters that moved around (as in animation) through a hidden system of wheels and levers.  The scenes would change from one to another after a certain time had elapsed, such as during the course of a spoken story.  This Wikipedia entry also points to some of the inventions by this man that I saw on the show.  These include an ancient temple "vending machine" where water would pour out after inserting a coin; a water fountain/pool which would constantly replenish itself after some of the water was removed; and a simulated bird chirping machine.  A number of his inventions were used for religious or temple purposes, and they must have amazed all who came across them (even if they didn't know of the engineering behind what they were seeing).But perhaps Heron's greatest invention was a kind of steam engine, or "aeolipile".  You can see a diagram of it here.  According to the show I watched, although Heron came up with this idea, he didn't really capitalize on it and I believe he died soon after making it.  I think that our conception of the steam engine wasn't put into use until the 18th Century.  However, can anyone imagine what it would have been like if Heron had survived long enough to apply his invention to a Roman cart or chariot?  Or think about a barbarian army facing a line of self-propelled Roman battle tanks.  This is one of those big "what ifs" of history that would have turned the tide of technology if it would have been realized.

Problem with Heron is that he existed in a time before science existed. He built things that were innovative - but they were not foundational, in the way that a microscope was when the science of microbiology was beginning....Or Tesla, who developed AC that began modern technology [i[per se[/i].

Well I guess it's two sides of a coin, then.  Whereas you see this as a detraction, I see it as an addition.  Since Heron arguably didn't have much "science" to rely upon, he was all  that much more of a trailblazer since he did it on his own.  However, I do think that he had to understand some of the basic principles of science in order to accomplish what he did.  I don't think it's any less of a feat to accomplish something without understanding the entirety of the science; I don't think that the Wright brothers understood all of the physics involved with aero-engineering when they built their first plane, but we don't think any less of them for it.