What is the difference between Ethereum and Chainlink?

Could you please elaborate on the fundamental differences between Ethereum and Chainlink? I'm particularly interested in understanding how they function differently within the cryptocurrency and blockchain ecosystem. Ethereum, I know, serves as a decentralized platform for smart contracts and distributed applications, leveraging blockchain technology. But what exactly does Chainlink offer that is unique, and how does it complement or interact with Ethereum? I'm also curious about the specific use cases where these two technologies might be employed separately or together. Your insights would be greatly appreciated.