Bitcoin Gold was created to reinstate a more decentralized, democratic mining environment that Bitcoin enjoyed in its early days. In context of escalating concerns over Bitcoin mining centralization and corresponding potential network abuse, Bitcoin Gold experiments with a new mining algorithm with the hopes of informing potential future changes to Bitcoin mining. Unlike some forks, Bitcoin Gold doesn't intend to overtake Bitcoin per se, but rather to draw attention to and experiment with possible solutions for enabling retail investors to participate in mining.
Bitcoin Gold forked from Bitcoin at block 491407. This fork implements a new proof-of-work (PoW) algorithm to replace SHA256, namely Equihash, to achiee "ASIC resistance", a point of criticism for status quo Bitcoin mining. In the white paper, Bitcoin Gold explains its readiness to hard fork if or when Equihash is vulnerable to ASIC miners. Also, Bitcoin Gold's difficulty adjustment algorithm (DAA) is different: DigiShield V3. This change is intended to protect the network from abnormal changes in difficulty from significant changes in total hash power. Instead of launching immediately after the "snapshot" of the original chain and crediting equal balances of the fork coins to original addresses, Bitcoin Gold officially launched a few days after the chain split.