A participant on a proof-of-stake (PoS) blockchain, involved in validating blocks for rewards.

What Is a Validator?

A validator is a crucial part of the Proof of Stake (POS) consensus mechanism whose responsibility is to verify blocks to earn rewards. 
The decentralized nature of blockchain technology makes it impressive and so promising that more and more people are adopting it. Every blockchain has building blocks that are called nodes. They are responsible for holding data but this data needs to be first validated or verified on the blockchain network. That’s where a validator comes into play.
There are two common validation protocols of a blockchain network, which are Proof-of-Work and Proof-of-Stake.

Much like a banker who is responsible for verifying a transaction before its processing, a validator verifies each incoming transaction. 

A transaction can only be completed and its record can be added to the blockchain once its accuracy and legal authenticity are checked—that’s done by a validator.

In the Proof-of-Stake mechanism, a validator determines whether or not a transaction conforms to the rules that deem it as valid. The entire process makes a blockchain network secure and transparent. 

PoW vs PoS 

Some blockchains work on the Proof-of-Work model for validation and some rely on the Proof-of-Stake method. For blockchains that follow the PoW method, miners solve complex mathematical problems—and other nodes cross-check that information - to earn rewards. This method requires miners to work as validators. The one who solves the puzzle first gets to add their block and receives rewards. 

But what is wrong with PoW? Well, mining isn’t the best solution due to its requirements as it needs specialized hardware for producing the required computational power—and consumes a lot of energy. 

Proof-of-Stake, on the other hand, doesn’t require specialized hardware or energy. This method focuses on the currency power by determining participation according to the coin supply.  The protocol selects the validators randomly in accordance with the staked coins. Validators in such a mechanism receive transaction or network fees as rewards.

In principle, both validation protocols share a common goal. However, Proof-of-Stake is considered to be safer and more efficient than Proof-of-Work.