His fans wanted to organize some kind of wake in his honor. After its initial success it became an annual event.
Extract from the proposal posted in the "Binary Freedom" forum by D Clyde Williamson, on Monday May 14, 2001 06:00am PDT:
Douglas Adams will be missed by his fans worldwide. So that all his fans everywhere can pay tribute to this genius, I propose that two weeks after his passing (May 25, 2001) be marked as "Towel Day". All Douglas Adams fans are encouraged to carry a towel with them for the day.
Make sure that the towel is conspicous- use it as a talking point to encourage those who have never read the Hitchhiker's Guide to go pick up a copy. Wrap it around your head, use it as a weapon, soak it in nutrients- whatever you want!
Because some time was needed to get the word out, Towel Day was organized two weeks after Douglas Adams' untimely death, on 25 May 2001.
Many other dates had been proposed. For those with an exceptionally long attention span: the 42nd day of the year ("Happy Adams Day"), 42 days after his death ("Second Day of Remembering"), the 11th of March (his birthday, around which from 2003 on a yearly "Douglas Adams Memorial Lecture" is held), the last Friday of every May, the Friday before the 42nd week-end day of the year (occasionally falls on 25 May, as it did the year he died), etc.
Of all proposed dates, the 25th of May turned out to be the one that gained a significant following.
As the universe that Douglas Adams created was full of absurdity and randomness, it may be a fitting choice after all. And if you need an additional reason: if you add the hexadecimal numbers 25 and 5, and convert the result to decimal, you get 42!
A towel, it says, is about the most massively useful thing an interstellar hitchhiker can have. Partly it has great practical value -- you can wrap it around you for warmth as you bound across the cold moons of Jaglan Beta; you can lie on it on the brilliant marble sanded beaches of Santraginus V, inhaling the heady sea vapours; you can sleep under it beneath the stars which shine so redly on the desert world of Kakrafoon; use it to sail a mini raft down the slow heavy river Moth; wet it for use in hand-tohand-combat; wrap it round your head to ward off noxious fumes or to avoid the gaze of the Ravenous Bugblatter Beast of Traal (a mindboggingly stupid animal, it assumes that if you can't see it, it can't see you -- daft as a bush, but very ravenous); you can wave your towel in emergencies as a distress signal, and of course dry yourself off with it if it still seems to be clean enough.
More importantly, a towel has immense psychological value. For some reason, if a strag (strag: non-hitchhiker) discovers that a hitchhiker has his towel with him, he will automatically assume that he is also in possession of a toothbrush, face flannel, soap, tin of biscuits, flask, compass, map, ball of string, gnat spray, wet weather gear, space suit etc., etc. Furthermore, the strag will then happily lend the hitchhiker any of these or a dozen other items that the hitchhiker might accidentally have "lost". What the strag will think is that any man who can hitch the length and breadth of the galaxy, rough it, slum it, struggle against terrible odds, win through, and still knows where his towel is is clearly a man to be reckoned with.
Hence a phrase which has passed into hitch hiking slang, as in "Hey, you sass that hoopy Ford Prefect? There's a frood who really knows where his towel is." (Sass: know, be aware of, meet, have sex with; hoopy: really together guy; frood: really amazingly together guy.)
2011 is the year of the 10th anniversary of Douglas Adams' death, but of the... 11th Towel Day! The confusion arises from the fact that the first Towel Day occured shortly after Douglas' death, long before the year of its first anniversary. Maybe this can help:
2001 - Towel Day #1 (year Douglas died)
2002 - Towel Day #2 (Douglas 1 year dead)
2003 - Towel Day #3 (Douglas 2 year dead)
2004 - Towel Day #4 (Douglas 3 year dead)
2005 - Towel Day #5 (Douglas 4 year dead)
2006 - Towel Day #6 (Douglas 5 year dead)
2007 - Towel Day #7 (Douglas 6 year dead)
2008 - Towel Day #8 (Douglas 7 year dead)
2009 - Towel Day #9 (Douglas 8 year dead)
2010 - Towel Day #10 (Douglas 9 year dead)
2011 - Towel Day #11 (Douglas 10 year dead)
2012 - Towel Day #12 (Douglas 11 year dead)
2013 - Towel Day #13 (Douglas 12 year dead)
1) Start as early as possible (this increases the chance that people will hear about it and show up)
2) Put enough effort in telling the world about it (same reason). Create a Facebook event or web page and share it. And don't forget to send an e-mail about your event to: info at towelday dot org, include the URL of your Facebook event or web page in your message
3) Keep your towel at hand and Don't Panic!
We'll link to the pictures of an event if you send us the URL where they can be found! Please don't send the pics themselves. We don't host pics and recommend to upload them on Flickr and tag them with "towelday", for maximum exposure.
Terry Pratchett fans who "wear the lilac" on Towel Day may wish to donate to the Alzheimers Research Trust of the UK. (Terry is a patron and an Alzheimers patient)
And here's a chance to help charity... for free:
The Hitchhiker's Guide to the Galaxy Foundation has been created in memory of Douglas Adams, to promote literacy and communication skills. They do not at this time accept donations, but YOU CAN help them by recommending small literacy or communication skills charities or organisations that they could support. Their e-mail address is info at hitchhikerfoundation dot org dot uk
If you're a hardcore hitchhiker, you may need something stronger than Towel Day. And yes, there is such a thing. Listen carefully, we will say this only once. What you are looking for is called ZZ9 Plural Z Alpha, the Hitchhiker's Guide to the Galaxy Appreciation Society. Beware, these folks are really weird. But then again, so are you.
On 16 May 2001 Chris Campbell and his friends registered towelday.org and created a website. People all over the world celebrated Towel Day and sent them pictures of themselves with their towels. After several celebrations the creators moved on to other projects, but...
In February 2004, Tobbe "Kojv" Landin relaunched the site on his own server at towelday.kojv.net! He kept the tradition alive and ran a rather successful online forum. But in late 2008 he unexpectedly died at the age of 30 and his site disappeared. All was not lost however, because...
Meanwhile, fans had bought back the original towelday.org domain from a domain squatter. Strapped for time, they started out with a minimal webpage, but they're gradually improving the site along the way.