Bitcoin Gold comes from a hard fork of Bitcoin which took place on October 24, 2017 at block 491,407. All people with BTC on this date received BTGs with a one to one ratio. Its purpose was to change the paradigm about the mining that existed until then with the BTC.
According to the founders of BTG, the original Bitcoin blockchain had become too centralized because mining is essentially the work of several big companies. This therefore went against the original spirit of the BTC which aimed to create a decentralized peer-to-peer exchange system. To resolve this concern, Bitcoin Gold has decided to implement changes that would make mining more fair by setting up a network where anyone can become a miner with only basic computer hardware. As a result, many individuals can now mine this crypto-asset, unlike BTC where only a few large companies are responsible for this process.