By going back in time, he changed history in that he galvanized Edison to work on AC. The DC timeline from whence he came no longer will exist.
Another vot for Benjamin Franklin.
Although I’m not sure if he was from the future or if he was just several thousand years old.
Another vote for Leonardo and Hero of Alexandria, also Archimedes.
There can be only one.
I’m pretty sure Tesla is from an alternate universe, not the future.
Or if he is a time traveler, he’s from 10,000 years from now and has no way to recreate their technology in Victorian times.
All part of the service. 
Or maybe he knows it is possible but struggled to recreate the required circumstances using ‘ancient’ technology.
That makes sense. All of his handheld devices operated on DC Battery power. The hot dog cart guy who accidentally stumbled into the high-energy [del]magic[/del]physics experiment had no idea how AC power worked, just that his iPhone could no longer charge.
What age range? I went to the same high school (Homestead High in Cupertino CA) as both him and Woz… I wonder if we know some of the same people?
I suspect Gene Rodenberry
Brings to mind Empedocles; stories about his efforts to combat disease via water purification came down to us, but a lot of his writings were lost, which is why we’ve largely just got Aristotle’s collected mockeries of the guy’s weird teachings – light takes time to travel, matter is made up of tiny particles under the sway of attractive and repulsive forces, it’s mere chance rather than godly design powering evolution by survival of the fittest – all interspersed with mention of how the dude would go on and on about the benefits of a vegetarian diet, or his equally matter-of-fact belief that we’re living in a cyclical universe that periodically comes back together into a ball only to explode outward and re-scatter, and so on.
Buckminster Fuller. In some ways, you’d think he was thinking of “The Jetsons” cartoon family, in others he was dead on target but may not have known it. I found him quite fascinating while in school.
Yeah, he was one of my faves as well. The Optimism! of the early sixties!
Half the time I thinking: “What a kooky dude” the other half I thught: “The hell? Did he have someone broadcasting back from the future?” There was a naive brilliance about some of his assumptions… yet remarkable naivety that went with it too, like a kid who is confident that one day the world really will be like Star Trek.
In Toronto a few years ago, they had an industrial design exhibit at the ROM that included some Dymaxion designs. I found them positively charming!
I hope Gene Roddenberry was from the future.
But I think it was Rasputin.
If the future produced him, I don’t want to go there.
I could buy this one, with a healthy dose of mistranslation in the interval. “No, the light streams into your eyes, not from your eyes! Dammit. I wish I’d studied more Greek and less Hanseatic wool routes.”
He had an idea to mold buildings wholesale out of concrete. It failed miserably. The middle school I went to was one of the ones he built. It was impossible to keep warm and very difficult to maintain when it was damaged.
Whoever it was who carved the stone in Egypt (Rosetta something). If I were to travel back in time, that’s just about all I’d do. Of course, I’d probably wind up burying the complete dictionary of Tocharian B somewhere in Southern Indiana, just to mess with everyone.