Casper is a new consensus algorithm that is being developed by the Ethereum Foundation. What makes Casper different from other consensus algorithms is that it uses a hybrid of proof-of-work (PoW) and proof-of-stake (PoS). PoW is the consensus algorithm that is used by Bitcoin, while PoS is used by Ethereum. The reason that Casper is being developed is because Ethereum is looking to move away from PoW. The main reason for this is that PoW is very energy intensive. It is estimated that the Bitcoin network uses as much energy as the country of Denmark.