The Genesis Block is the hard-coded starting point of Bitcoin’s blockchain. Its coinbase data contains a headline from The Times: a timestamp and a pointed reference to bank bailouts.
Block 0 has no predecessor and its original 50 BTC output cannot be spent through the normal transaction database. Later blocks build on its hash, establishing the history that nodes independently verify.
The newspaper text proves the block could not have been created before 3 January 2009. It is widely read as commentary on discretionary rescue of the banking system, although the protocol itself does not encode a political interpretation.
For the clearest picture, read this entry together with Bitcoin, Satoshi Nakamoto, Bitcoin Whitepaper, Block Subsidy, Timechain. The reverse links also lead from Bitcoin, Satoshi Nakamoto, Timechain, Block Subsidy.