It is used to generate the genesis block, from which all other blocks ultimately derive. Presumably Satoshi has the private key for that txout, but it's unspendable anyway.

https://blockchain.info/block/000000000019d6689c085ae165831e934ff763ae46a2a6c172b3f1b60a8ce26f

https://blockchain.info/tx/4a5e1e4baab89f3a32518a88c31bc87f618f76673e2cc77ab2127b7afdeda33b