Bitcoin core helps to keep it decentralized and is programmed to decide which block chain contains valid transaction
Bitcoin core was created by Satoshi Nakamoto in the late 2008 and is the original implementation of Bitcoin.
  It is invariably a wallet for storing bitcoins and the node of the Bitcoin network. The wallet allows for storage, sending and receiving of Bitcoin.

Bitcoin protocol  https://www.researchgate.net/figure/Example-of-the-bitcoin-protocol_fig1_299368011
 Can Bitcoin core operate without the protocol or do they work hand in hand.