Is Ethereum USDT or USDC?

I'm quite puzzled here. Could you possibly clarify for me whether Ethereum is associated with USDT or USDC? I've been hearing a lot about both of these stablecoins, but I'm not quite sure how they relate to Ethereum, if they do at all. I understand that Ethereum is a blockchain platform that supports smart contracts and decentralized applications, but does it have any direct connection to USDT or USDC? I'm really trying to wrap my head around this cryptocurrency landscape, and your explanation would be greatly appreciated.