The WHATWG (Web Hypertext Application Technology Working Group) is an organization that maintains and develops HTML and APIs for Web applications. Former employees of Apple, Mozilla, and Opera established WHATWG in 2004.
Specification editors at the WHATWG research and gather feedback for the specification documents. The group also has a small committee of invited members authorized to override or replace specification editors. You can join as a contributor by signing up for the mailing list.