To some he is a hero fighting a one-man crusade against grammatical sloppiness.

Others insist his work is “comprised of” 47,000 pointless “corrections” that make him the internet’s most obsessive and irritating pedant.

To many whom he has edited, he is known only by his pseudonym “Giraffedata”. But now he has been unmasked as Bryan Henderson, a 51-year-old software engineer from San Jose, California.

His target – his only target – is the two-word phrase “comprised of”. Plenty of people – respected authorities on grammar among them – consider the phrase acceptable in contemporary usage, but Mr Henderson says it is wrong.

So, since December 2007, he has made it his mission to find every instance of its use on Wikipedia and edit them out.

Other Wikipedia users may have clocked up more than Mr Henderson’s 47,000 edits – the encyclopaedia’s most prolific editor has managed 1.45 million edits and counting. But, Mr Henderson says proudly, “I’m the only one who concentrates on one aspect [of grammar]”.

He is also one of a select band whose dedication (or pedantry) once prompted a direct appeal for “intercession” to the founder of Wikipedia, Jimmy Wales. “Even though numerous editors have objected to his obsessive removal of the grammatically acceptable term, he defiantly continues to do so,” pleaded a disgruntled Wikipedia contributor in June 2009.

But Mr Wales did not intercede. “I believe that Giraffedata’s arguments are persuasive,” he said, while stressing: “I am expressing no opinion on how the change is being implemented.”

Every Sunday before bedtime, Mr Henderson runs his own self-written software programme allowing him to hunt down the phrase.

As he revealed himself to the world via an interview with the website Medium.com, Mr Henderson said that he has got so efficient that an edit normally takes him just 10 seconds. At one stage, in August 2010, he had removed every one of the 18,000 occurrences from Wikipedia. Then he found he had to keep going because 70 new examples of the phrase were appearing on the site every week.

Mr Henderson insists he does have a life, telling one Wikipedia user: “I have a full time job and numerous hobbies.”

To the trickier question – what’s wrong with “comprised of”? – his basic argument seems to be that: “To comprise means to include, as in, ‘The 9th district comprises all of Centerville and parts of Easton and Weston.’ And thus: ‘The 9th district is comprised of ...’ is gibberish. The phrase apparently originated as a confusion of ‘comprise’ and ‘composed of’.”