Eric S. Raymond
Eric Raymond wrote the highly influential book The Cathedral and the Bazaar, explaining the key advantages of the emerging open source community development models in terms that people understood deeply.
In the late 1990's Eric Raymond and others developed the term "open source" as a more business friendly term than "free software", with a more inclusive meaning where licenses that were not as strict about the passing on of modifications would also quality for the term.
The Open Source Initiative was established at the great domain name OpenSource.org. Among the OSI's greatest contribution to the field has been their promotion of the open source ecosystem, and their certification of licenses that were truly open. However, by 2007 Commercial Open Source Software had effectively co-opted the term, leading the community to develop the term FOSS to bring the original visions back together.
Eric contributed to a wide range of projects.