The CryptoPunks are 10,000 uniquely generated characters. No two are exactly alike, and each one of them can be officially owned by a single person on the Ethereum blockchain. Originally, they could be claimed for free by anybody with an Ethereum wallet, but all 10,000 were quickly claimed. Now they must be purchased from someone via the marketplace that's also embedded in the blockchain. Via this market you can buy, bid on, and offer punks for sale.
