$BTC

In short, Bitcoin was designed as a digital currency, with a finite supply, based on mathematics and cryptography, in a transparent, distributed, and decentralized system, to eliminate the intermediary (in traditional currency, banks or governments). In practice, there is much more to it, but that is essentially the fundamental nature of what Bitcoin is.

Satoshi Nakamoto first published it as a technical document in 2008, a pseudonym, as to this day, no one has come forward and conclusively claimed or proven to be Nakamoto. What was unique or novel about the approach highlighted in the technical document was the use of distributed computing technology and a network protocol to essentially enable direct cash transactions, from person A to person B, without the need for an intermediary. Furthermore, the nature of these transactions, recorded and maintained in a transaction ledger, would be distributed and transparent, eliminating the classic "double spending problem" inherent in digital assets.