Bitcoin is the original cryptocurrency. It was first laid out in this 2008 whitepaper (https://www.coinbase.com/bitcoin.pdf) as a digital money that allows for secure peer-to-peer transactions on the internet. Every transaction involving Bitcoin is tracked on the blockchain, which is similar to a bank’s ledger, or log of customers’ funds going in and out of the bank. In simple terms, it’s a record of every transaction ever made using bitcoin. The volume of bitcoin is capped at 21 million, although there is now heavy trading in fractional coins.
Who is behind this? Satoshi Nakamoto - there is speculation that this may be a pseudonym for another person or group who wrote the whitepaper.
Bitcoin Whitepaper (https://www.coinbase.com/bitcoin.pdf)