The historical figure that strikes me as "most likely to be a time traveller" is Archimedes, who designed incredibly advanced machines that destroyed the Roman fleet and protected his home city. Sadly he was accidentally killed during the war. The Romans wanted to capture him and use him for their own purposes. It's possible that could have changed history quite a bit.
Heron of Alexandria is another candidate that gets a lot of space in that book. He invented the first steam engine way before his time. But also many other insanely elaborate mechanical devices. Including an entirely mechanical little theater, with mechanical puppets and music.
Unfortunately almost all his inventions were for entertainment value only. Sometimes I wonder if the greatest inventor of our time might be applying his work to video game engines.
Perhaps an "Ask HN: Books that are not programming" might turn up some handy hints?
I guess now you have this book you look on Amazon for other books that people have bought or looked at?
My recommendation: (http://www.amazon.co.uk/Ancient-Inventions-Wonders-Peter-Jam...) - it's pop.sci but entertaining.
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