In 1985, Research Software Ltd. made a language called Miranda, that's where the beginning is... In the following years, more and purer functional languages where coming out, but most widely-used one was Miranda, unfortunately, it was proprietary.
Conference on Functional Programming and Computer Architecture took place here. The Discussion was about the unfortunate situation in the functional programming community: there had come into being more than a dozen non-strict, purely functional programming languages, all similar inexpressive power and semantic underpinnings. There was a strong consensus at this meeting that more widespread use of this class of functional languages was being hampered by the lack of a common language. Then, people decided that a committee shall be formed to design such a language, providing a new experience in functional programming. After a few years of work, the committee published the first Haskell Language Report in 1990. That was the major milestone. The same year, Haskell 1.0 was released. The work resulted in a series of language definitions, 1.0, 1.1, 1.2, 1.3 and 1.4. After other several years of works on Haskell, in late 1997, the series culminated in Haskell 98. In February of 1999, the Haskell 98 language standard was published as 'The Haskell 98 Report' and it was refreshed in January 2003 as 'Haskell 98 Language and Libraries: The Revised Report'. The language continued to evolve rapidly with the Glasgow Haskell Compiler (GHC). In 2006, the successor to the Haskell 98 was started to be defined, informally named Haskell Prime. This was intended to be an ongoing incremental process to revise the language definition, producing a new revision up to once per year. The first revision was announced in November 2009, published in July 2010, named Haskell 2010, the latest stable update, but Haskell 2020 is announced.