The underlying impetus to develop Ethereum and consequently Ether was to utilize aspects of the technology initially developed as part of the Bitcoin blockchain and combine it with the capabilities of smart contract technology. The idea was that this marriage would lead to a platform that could sustain not only the money or medium of exchange use case, but also to add programmability to money, introducing conditional logic to the equation that would open up a world of possibilities with regards to decentralized financial applications and products, and additional decentralized applications.
The Ethereum presale took place from Tuesday, 22 July 2014 to Tuesday, 2 September 2014, lasting a total of 42 days. The price of ether was initially set to a discounted price of 2000 ETH per BTC, and stayed that way for 14 days before linearly declining to a final rate of 1337 ETH per BTC.
60 Million ether was created for the presale of which 80% was available for purchase with 20% (or 12 Million) being retained by the Ethereum Foundations 'development fund' which consisted of early contributors to the project and developers.
The presale ended with ~31,000 BTC (equivalent to ~$18.3 million) being raised by the Ethereum Foundation over the 42 days.
Ether was not usable or transferable until the launch of the genesis block which occurred on July 30th, 2015.