Besides the answers, you can actually mine your own genesis block, by the same way you mine non-genesis blocks, when you mined your own genesis block, you are essentially creating a new coin and blockchain.
You can refer to
https://bitcointalk.org/index.php?topic=181981.0 for a simple program on how to mine genesis blocks.
Interesting. I'm trying to learn more about the technical side of Bitcoin. So does this mean Satoshi mined the Genesis block? Meaning, did he actually use computing power to mine the Block? Or was the genesis block instamined when the network went live?