A software developer called Satoshi Nakamoto proposed Bitcoin which was an electronic payment system backed not by the gold standard or the dollar but by open source mathematical formulas that enabled instant transfers with very low transaction fees.
3. Who prints it?
No one. The currency isn't printed by some shadowy bankers intent of paying off national debt effectively devaluing their currency and causing economic crises. It is instead created digitally by a community of people that anyone can join who 'mine' it using computation power when they process transactions made virtually in the system. Basically, bitcoin are only generated to pay the people who diligently watch the blockchain and verify transactions.
4. How many coins exist today?
The bitcoin protocol - the rules that make it work, say that only 21 million bicoins can ever be created by miners. These coins can however be divided into smaller parts with a Satoshi (named after the founder) being the smallest available at one hundredth of a bitcoin - like one cent to a shilling.