They are commonly called aggregators (or attestors/aggregator validators in many Proof‑of‑Stake systems like Ethereum).

Quick Scoop: What Are These Validators?

In modern Proof‑of‑Stake blockchains, not all validators do the same job at every moment. Some propose blocks, some simply vote on them, and a special subset takes on the job you’re asking about.

These special validators:

  • Collect individual signatures (attestations) from other validators.
  • Aggregate those signatures into a single compact signature.
  • Attach this aggregated signature to the block header.
  • Receive extra rewards for doing this extra coordination work.

The Term You’re Looking For

In most technical docs and discussions:

  • The validators that collect and add signatures to a block (or block header) are called aggregators.
  • The act they perform is aggregation of attestations or signatures.
  • They are still validators, but with a temporary special aggregator role selected by the protocol for a given slot or round.

A simple way to phrase it for forums:

The validators that gather signatures from others, merge them, and attach the result to the block header (earning extra rewards) are called aggregators.

Mini Story Example

Imagine a PoS network with 1,000 validators:

  1. One validator is chosen as the block proposer to build a new block.
  1. Hundreds of other validators check the block and sign off on it (their signatures are called attestations).
  1. A few special validators are randomly chosen as aggregators.
    • Each aggregator collects many attestations from others,
    • Compresses them into one aggregated signature,
    • Adds it to the block header or consensus message,
    • Broadcasts this to the network and earns additional rewards for this service.

So in Q&A form:

  • Question: What do we call the validators that collect and add signatures to the block header and receive additional rewards?
  • Answer: They are called aggregators (aggregator validators).

TL;DR: In PoS systems, the validators that gather others’ signatures, aggregate them, attach them to the block header, and earn extra rewards are known as aggregators.

Information gathered from public forums or data available on the internet and portrayed here.