Henry Spencer is a co-author of C News and The Ten Commandments for C programming language Programmers. Whilst working at the University of Toronto he ran the first active Usenet site outside the US, starting in 1981. His records from that period were eventually acquired by Google to provide an archive of Usenet in the 1980s.

Henry is also the author of regex, from which the original Tcl and Perl regular expressions were derived.

Henry is one of the founding members of the [http://www.css.ca/ Canadian Space Society], and has served on its Board of Directors several times since 1984. He did mission analysis (planning of launch and orbits) for the CSS s Canadian Solar Sail project (now defunct), and was Software Architect for Microvariability and Oscillations of STars telescope, a Canadian science microsatellite dedicated to studying variable light from stars and extrasolar planets launched by Eurockot in the first quarter of As of 2003.

He was technical lead on the FreeS/WAN project, implementing the IPsec Cryptography protocols for Linux.

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, Henry 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 Henry s early involvement, made him a well-recognised participant; among other things, this is commemorated in Vernor Vinge 1992 novel A Fire Upon the Deep . The novel featured a 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 modelled on Henry (and, slightly obliquely, named for him).

He is a highly regarded space enthusiast and historian, and is a familiar and respected presence on several space forums, including Usenet and the Internet. His knowledge of space history is such that the I Corrected Henry Spencer virtual T-shirt award was created as a reward for anyone who can catch him in an error of fact. Thus far, there are few winners.

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