Dapper Labs’ CryptoKitties are seminal NFT crypto collectibles. While there are older collections (such as CryptoPunks), CryptoKitties were the first NFTs to be minted using Ethereum’s ERC-721 token standard, and their popularity quickly congested the network. Now, amidst the recent NFT market resurgence, some of the oldest CryptoKitties are in hot demand again.
Source: Remember CryptoKitties? Classic Ethereum NFTs Are Soaring in Value – Decrypt