Bitcoin Gold Hard Fork was shown on October 24, 2017 at Block 491,407 of Bitcoin Blockchain. Bitcoin Gold took a snapshot of the bitcoke block chain at that altitude, as is common in hard-fork, and kept all transactions and balances up to that point, then started its own block chain
As decentralization becomes more important, resistance to ASICs is becoming increasingly important to some cryptographic callers. Bitcoin Gold is specifically designed to make Bitcoin ASIC resistant and dispersive.