The concept of digital money started at the beginning of the 1980s with David Chaum’s contribution. Almost one decade after, Nick Szabo introduced the idea of “smart contracts” : programmable contracts that allow the trust-less execution of codified terms without the need for a third party. In 2007 Satoshi Nakamoto started working on Bitcoin, and eight years after Vitalik Buterin, Mihai Alisie, Anthony Di Iorio, Charles Hoskinson, Amir Chetrit, Joseph Lubin, Gavin Wood and Jeffrey Wilcke founded Ethereum. The Ethereum system aims to be the best network to generate smart contacts.
In their 2013-White Paper the founders of Ethereum detailed a roadmap divided in four main phases : Frontier, Homestead, Metropolis and Serenity. 2020 is considered by the majority of the community as the beginning of Serenity and therefore to be close to the achievement of the final and complete Ethereum network.
Source : Kraken’s into the Ether, A Concise Primer on Ethereum