The first block in the blockchain is called the genesis block. It is the common ancestor of all the blocks in the blockchain, meaning that if you start at any block and follow the chain backward in time, you will eventually arrive at the genesis block. Every node always starts with a blockchain of at least one block because the genesis block is statically encoded within the bitcoin client software, such that it cannot be altered.
Trivia: Bitcoin’s genesis block was created in 2009 and contains a hidden message within it: ”The Times 03/Jan/2009 Chancellor on brink of the second bailout for banks.” It’s a symbolic pointer to the dangers of centralized issuance of national currency in the midst of the worldwide financial crisis.
Additionally, the Bitcoin genesis block was created with 50 coins in it, which are unspendable. It has been debated whether this was intentional on the part of Satoshi Nakamoto, or an oversight. The Bitcoin genesis block also took 6 days to mine, which is strange considering since then each new block takes approximately 10 minutes to mine. There is no consensus regarding why the genesis block would have taken so long to mine.