What is Collator (Polkadot)?

Collators are full nodes on the Polkadot Network that are present both on parachains and the main Relay Chain. Their main purpose is to maintain parachains (which are sovereign blockchains or specialized shards) by collecting parachain transactions and producing state transition proofs (essentially machine-driven progress reports) for validators on the Relay Chain. Collators can access all state transition information necessary for authoring new blocks and executing transactions — much like how miners provide value in a Proof-of-Work system. Collators are also used to send and receive messages from other parachains, facilitating communication through Cross-Chain Message Passing (XCMP).