Henry Spencer is a Canadian computer programmer and space enthusiast. He wrote "regex", a widely-used software library for regular expressions, and co-wrote C News, a Usenet server program. He also wrote The Ten Commandments for C Programmers. He is coauthor, with David Lawrence, of the book Managing Usenet. While working at the University of Toronto he ran the first active Usenet site outside the U.S., starting in 1981. His records from that period were eventually acquired by Google to provide an archive of Usenet in the 1980s.
The first international Usenet site was run in Ottawa, in 1981; however, it is generally not remembered, as it served merely as a read-only medium. Later in 1981, Spencer acquired a Usenet feed from Duke University, and brought "utzoo" online; the earliest public archives of Usenet date from May 1981 as a result.
The small size of Usenet in its youthful days, and Spencer's early involvement, made him a well-recognised participant; this is commemorated in Vernor Vinge's 1992 novel A Fire Upon the Deep. The novel featured an interstellar communications medium remarkably similar to Usenet, down to the author including spurious message headers; one of the characters who appeared solely through postings to this was modeled on Spencer.