Does the creator of BitCoin hold a 'master' private key?
No one holds a key that gives them special control of the blockchain.

The closest thing to a "master key" was the alerts system, which allowed signed messages to be sent to every client, for example, to tell users to update their client in response to a security issue.  This feature was for alerts only and can in no way affect the blockchain, transactions, or user balances.  This key was possessed by Satoshi, Gavin Andresen, and theymos.

Update: The alerts system was retired in the summer of 2018, due to risk of DOS attack vectors (full nodes could be DOS attacked by carefully crafted alert messages), and increasingly widespread knowledge of the alert keys.