No one. Miners compute cryptographic hashes based on the previous block in the blockchain plus a nonce. If the hash starts with a number of zeroes (currently

No one. Miners compute cryptographic hashes based on the previous block in the blockchain plus a nonce. If the hash starts with a number of zeroes (currently 7), it is considered valid and the miner who computed it is rewarded with a chunk of bitcoins by the network. Only 21M BTC will ever be mined (although each BTC is composed of 10^8 Satoshis, which are the actual "unit" of transaction). As more BTC are mined, the difficulty of finding new ones increases and the reward decreases. Once the difficulty goes up, only those hashes that begin with 8 zeroes will be considered valid, so it will take twice as much effort to find a valid one. Currently, a successful block nets 25 BTC to the miner, down from 50 a while back. Soon, it will drop to 12.5 BTC. Bitcoin is, by design, deflationary. All other things being equal, the value of a Bitcoin will continue to rise as the pool of unmined coins shrinks. There is no central authority, rather inherent scarcity and the effort required to mine the coins gives value. The exchange rate of BTC -> fiat is determined by the market, operating on exchanges such as Mt Gox. There is no mechanism for anything outside of market effects to alter the price or availability of Bitcoin.