What Is a ‘Builder’ and a ‘Proposer’ in the Context of MEV and Transaction Ordering?

In Ethereum's Proof-of-Stake system, the process of block creation is split into two roles: the builder and the proposer. The builder is responsible for assembling a block of transactions, often including profitable MEV bundles from searchers.

The proposer is the validator randomly selected to propose the next block to the network. The proposer chooses the block with the highest bid from a builder.

This separation, known as Proposer-Builder Separation (PBS), was introduced to mitigate the centralization risk of MEV.