Wrapped Bitcoin (WBTC) is an ERC20 token backed 1:1 with Bitcoin.
This community-driven token aims to standardize Bitcoin to the ERC20 format, creating smart contracts for Bitcoin.
The proof of reserve is on-chain, which shows the exact 1:1 between minted WBTC tokens and Bitcoin stored by the custodians. When WBTC token holders redeem their tokens for Bitcoin, the tokens are burned. The mining and burning of tokens are in turn tracked and verifiable on the blockchain.