Ethereum's roots stem from Bitcoin. Bitcoin made one major innovation: decentralized trust. Conventionally we trust governments or companies.
Bitcoin moved trust to the network.
With that, the first decentralized currency was born. But a currency is limited. Now enter Ethereum.
Ethereum is a single computer we can trust.
Using Ethereum we can remove middlemen that make money providing trust. Companies like eBay get replaced with trusted programs built on Ethereum. A seller, buyer, and insurance provider all interact directly with the Ethereum computer.
Be it for banks, governments, crowdfunding, or record labels, Ethereum is the most powerful mediator in human history.