There are many answers to these questions. My main goal here today is to explain most of them without being a diffident jerk to Edison. Let's begin.
Nikola Tesla (variants include Nicola and Nikolai) was born in Croatia, the land of ties. (It's also where Marco Polo was born.) Today we consider him Serbian because of where he lived but Croatia and Serbia are pretty dang close and he was born in the boundaries of modern-day Croatia. Here's a map to show you, those borders get pretty complicated. They do to me, at least. Europe can be so small...
moved to the United States. He ended up at the company of the inveterate opportunist Thomas Edison, which would lead to the most dramatic rivalry of all time, worse than Union/Confederate, Frost/Nixon, Vader/Obi-Wan, Rob/MysteriousRob, etc.
The most depressing aspect of it all was when Edison offered Tesla 25,000 dollars to fix his machines. That was a lot of money back then. It still is. When Tesla finished fixing the machines, he asked Edison for his money. Edison just clapped the Croatian on the back and said, laughing,
Tesla, you don't understand our American humor.
I don't mean to vilify Edison - he was quite the entrepreneur, and besides, The Oatmeal did a pretty damn good job of that already - but that's EVIL! Really evil. More evil than making a handless person clap, or a mute person talk, or a deaf person to hear. It just isn't RIGHT! In fairness (but was it?) he did offer Tesla a ten dollar raise. Tesla, understandably, left.
Tesla was obsessive-compulsive and rather insane. (That's a good thing.) He was obsessed with the number four (he would walk around a building four times before entering) and he had a fierce hatred of round objects. He could speak 8 languages, memorize entire books in his head, do calculus in his bloody mind, and much else. (I've got the second one down, but why must you make me feel so inadequate, Tesla?)
Lots of die-hard geeks (cough cough) know him for the Tesla coil, which is basically an electric curcuit that produces alternating current, or AC electricity. Today it powers pretty much everything we have. (Side note: Edison hated Tesla for having used AC, so he used his influence to electrocute people with AC to show the dangers of it. Hypocrisy. Edison was in favor of the far more vastly inferior DC, direct current, which is much weaker. In the end AC won, huzzah.) Tesla coils operate at extremely vast amounts of energy, so one must be careful.
So, what else did the inveterate genius create? Forerunner of radio, X-rays, and a lot more. He eventually had over 800 patents, which isn't bad.
He died at age 86, the end of a rather charging life (lame pun). One thing to note is that he remained celibate his entire life, citing "his work" as more important. That's true devotion to your job.
It goes without saying that Tesla was the most insane, weird, quirky, brilliant, awesome scientist ever. Edison's not even close to him.
Sources: The Oatmeal (fact-checked everything, though)
Badass of the Week
My own library of books (namely: Schott's Miscellany and New York Times Guide to Essential Knowledge)