The original Bitcoin (BTC) is Bitcoin. The code for Bitcoin is open source and 1000's of projects have forked Bitcoin code and did their own thing with it - deciding their own name, block times, block sizes, transaction costs, circulation, halvings, etc. In fact at the time of this writing there have been almost 30,000 copies of Bitcoin forked into new projects. Here is a link to the original Bitcoin repository and actively supported code. > https://github.com/bitcoin/bitcoin
Some individuals figured out that they could not only fork the bitcoin code but then they could also fork the ledger and the name which resulted in anyone who had Bitcoin at the time of the fork, also owning the same amount of the new flavor of Bitcoin. Most of these individuals and small groups managed to generate billions of dollars of value over night based on the reputation of the original developers and then proceed to try to perform a coup on the original developers while confusing new comers to crypto with a mini bitcoin identity crisis.
While its encouraged to fork the code of a successful project, general consensus is that it is black hat activity to also fork the ledger and name and especially in an effort to overthrow the original developers.
Other flavors of Bitcoin such as bitcoin gold, bitcoin cash, bitcoin cash sv, bitcoin diamond, etc - should not be seen as related to the original Bitcoin project in any way. These copies of Bitcoin should not be considered a cheaper "alternative Bitcoin" that will go up to the same price as Bitcoin. At the time of this writing, Bitcoin is the lead "digital currency" and it wont likely be replaced by a copy of itself if it can even be displaced from the top at this point.
Bitcoin may be the leading crypto currency intended for digital commerce but it isn't #1 in decentralized compute, storage, smart contracts or an array of other purposes. To see the leaders in their sectors, refer to our sector indices where you can compare sectors for blockchain adoption and an assets domination within their own sector. Sector Indices for crypto > https://coinmarketflow.com/indices/global