What is the name of the first major hard fork of Bitcoin?

The first major hard fork of Bitcoin was Bitcoin Cash.

Bitcoin Cash split from Bitcoin on 1 August 2017 during a long-running dispute over how the network should scale. Supporters of larger on-chain blocks argued that increasing block capacity could allow more transactions and reduce reliance on off-chain systems. The Bitcoin Cash chain launched with larger block-size rules, while the original Bitcoin chain retained its existing approach.

The split occurred at Bitcoin block 478,559, after which the two networks followed different consensus rules. Bitcoin holders who controlled coins at the fork generally received an equivalent amount of Bitcoin Cash on the new chain, although accessing those coins required compatible software and careful attention to replay and security risks.

Bitcoin Cash is often confused with later forks. Bitcoin Gold launched in October 2017, Bitcoin Diamond in November 2017, and Bitcoin SV split from Bitcoin Cash in November 2018. Earlier Bitcoin software incidents caused temporary chain splits or hard forks, so “first major hard fork” means the first prominent, lasting fork that created a separately traded Bitcoin-branded cryptocurrency—not the first protocol bug or incompatible software release.